Updated the API to work with the generic key `K: Encode` instead of the old `Key`.
Also, the change contains optimization to reduce the size of contracts. In most cases, it is `#[inline(always)]`; but `return_value` also got small optimization; removed usage of `extract_from_slice` where it is not needed.

Removed old 32 bytes `Key`. Replaced it with `u32`. Added `KeyComposer`, it is a helper struct that does all manipulation with the storage key. It allows concat two storage keys into one, compute storage key for fields based on the filed, struct, enum, variants names.
Removed all tests and benches. Didn't add it for new primitives because the key is standard `u32` and all keys are calculated during compilation.

storage crate:
Removed `SpreadLayout`, `PackedLayout`, `SpreadAllocate`, `PackedAllocate`, and all related helper functions.
Removed `Packed` struct cause it is the default behavior for storage right now. Added `Lazy` struct that allows `get`/`set` value from/into the storage. It is similar to `Mapping` but works with one storage key and one value.
Introduced new main traits to work with storage in `storage/src/traits/storage.rs`.
Also added a new `OnCallInitializer` trait to improve the flow with upgradable contracts and support initialization on demand by default. Added `pull_or_init` macro that inits the storage struct if it is impossible to load it. It also can be used as optimization for contracts without an explicit constructor.
Replaced implementation of old traits for main primitives with a new one. Added blanket implementation of new traits for structures that are `Packed` by default. It reduces the amount of code and adds support of generic structures but adds problems with tuples(now tuples implement new traits only if inner items are `Packed`).
Introduced `AutoKey` and `ManualKey` that allows specifying which key the user wants to use. Added support of it into all traits and structures.
Refactored `Mapping` to follow new rules.

Updated storage layout in the metadata. Introduces the concept of roots and leafs. Root defines the storage key for all sub-tree until there will be another Root. Leafs are common types that are part of the sub-tree and serialized/deserialized together into one storage key.
Replaced 32 bytes storage key with `u32`.
Added validation that all root storage keys don't overlap. Maybe better to add that error or reuse that validator on the `cargo-contract` side to show a more user-friendly error.
`RootLayout` and validator are used in codegen(next commit). The contract is wrapped into `RootLayout`, and we do validation for that tree.
Metadata now contains name for each struct/enum/variant/field. It is useful information because now the storage key is calculated based on the name of struct/enum/variant/field.

storage crate:
Added a new helper crate `storage/codegen`. It contains some useful functional that is used in `ink_storage_derive` and in `ink_lang_codegen` crates. It has a method that returns all types of the struct/enum/unit and a method that finds "salt" in the generics of the struct/enum. It uses magic constant "KeyHolder"(about that you can read in issue) to find salt, so I tried to have only one place where we are using that constant.

Replaced derive implementation of old trait with new one. You can check the tests to see how the implementation looks like. `Storable` recursively call `encode` and `decode` for all fields. `KeyHolder` return key of the salt. `Item` uses `AutoKey` or key specified by the user. I want to highlight that `PreferredKey` only is used with the `AutoItem` trait. If `PreferredKey` is `AutoKey`, then `AutoItem<AutoGenerated>` select auto-generated key, otherwise preferred. So `AutoItem` trait decides that key to use. It is why derive macro only set `PreferredKey`.
Updated drive for `StorageLayout`, now it uses `u32` and pass name of the struct into metadata.

…w the codegen uses `pull_or_init` in the `call`. Updated `execute_constructor` to work with new storage methods.

Allowed usage of generics during the declaration of the primary contract storage. Users can specify the default storage key with `KeyHolder` via generic.
Added parser for `storage_item` macro with its config.

…object implements `Decode` and `Encode`, it is `Packed`, and it uses the blanket implementation of new traits.

In dispatch, codegen started to use a new method to work with storage.
In metadata codegen added usage of new `RootLayout`. We wrap the contract into that layout because the contract has its storage key for all inner fields by default. Also added a run of validation logic during metadata generation.
Added `storage_item` macro. It transforms all types from autokey into manual key(if types support it). It calculates the storage key based on the name(it uses the `KeyComposer::compute_key` function from the primitives crate). Also, macro generates an additional `Check` structure that includes all raw fields. It helps show correct errors to the user in case of typos, wrong types, etc.

Simplified delegate call example very well causes of new `OnCallInitializer` trait and support of manual specifying key.

Can't highlight something unusual here=)

- In most cases it is comments=)
- Moved `pull_or_init` on one level upper.
- Put the tests into the `impls/mod.rs`

Add UI test for double storage_item.
Applied suggestion from the review.

# Conflicts:
#	crates/lang/codegen/Cargo.toml
#	crates/lang/codegen/src/generator/metadata.rs
#	crates/lang/macro/Cargo.toml

# Conflicts:
#	crates/lang/macro/Cargo.toml

Removed `delegate-call` example with `OnCallInitializer`

…ork-new-hope

# Conflicts:
#	.gitlab-ci.yml

…ork-new-hope