* Initial SMT store type

SMT (Sparse Merkle Tree) is intended to replace IAVL. New type
implements same interfaces as iavl.Store.

* Add iteration support to SMT

Sparse Merkle Tree does not support iteration over keys in order.
To provide drop-in replacement for IAVL, Iterator and ReverseIterator
has to be implemented.
SMT Store implementation use the underlying KV store to:
 - maintain a list of keys (under a prefix)
 - iterate over a keys
Values are stored only in SMT.

* Migrate to smt v0.1.1

* Extra test for SMT iterator

* CommitStore implementation for SMT store

* Use interface instead of concrete type

* Add telemetry to SMT store

* SMT: version->root mapping, cleanup

* SMT proofs - initial code

* Tests for SMT store ProofOp implementation

* Fix linter errors

* Use simple 1 byte KV-store prefixes

* Improve assertions in tests

* Use mutex properly

* Store data in ADR-040-compatible way

SMT stores:
 * key -> hash(key, value)

KV store stores:
 * key->value in "bucket 1",
 * hash(key, value) -> key in "bucket 2".

Outline of new store following ADR-040 pattern of decoupled
commitment/data concerns

Largely adapted from store/ll-smt branch

- Move tm-db code in from external repo
- Refactor store/ and types/ packages
- leaves out IAVL and multistore code pending confirmed deprecation
- some hacks to glue existing tmdb usage and get compile/tests working

- Update to new db interface
- Use smt as SC structure
- Refactor smt to BasicKVStore