feat: Native Merkle Trees

[PhilWindle]

This PR is the first of several where we are moving to use native implementations of Merkle Trees for performance reasons. It includes:

1. The core tree implementations for both indexed trees and append only trees.
2. The introduction of LMDB as a dependency that we retrieve from GIT and build ourselves.
3. The creation of a set of RAII wrapper objects around the LMDB concepts.
4. The creation of a committed/uncommitted store on top of LMDB used by the trees for state management