Delegate calls fix

[Artemka374]

Right now delegate calls can't work as they were before due to latest ink! changes.
As was mentioned in this issue, the problem is in initializing storage, so, we have the following possible options of making everything work:

• Using an empty ink(storage) struct and wrapping the main storage into another structure with initializing in Storable::decode method
• We can implement custom Storable::decode method, so every struct will be extracted from storage by it's own storage key and initialized if it is not, like it was implemented here, but we have a problem, that we can reimplement encode method for structs to be set to storage by theirs storage key by default, so we will need to manually flush every such struct in storage.
• Using Lazy for every such struct, but the downsides of this approach is that it will change the approach of working with any contract a lot

The best solution for this problem will be implementing something like this in ink! itself.

[PierreOssun]

@Artemka374 Will this be fixed by #76?
Any update on when can we have diamond contracts back ?