Webb-Solidity package structure

[nepoche]

This PR changes the project structure to separate packages:

• contracts: types of the latest solidity contracts
• fixed-bridge: Wrapper-classes for anchors, bridges, etc. related to fixed-bridge.
• tokens: Wrapper-classes for token functionality
• utils: Common utilities e.g. toFixedHex and others.
• vbridge: UNIMPLEMENTED, wrapper-classes for anchors, bridges, etc. related to variable bridges.

This PR brings in a dependency on lerna for building and publishing the packages.

This PR updates the root-directory package.json to include:

• yarn build:packages - needs to be run before tests.
• yarn compile - should be run instead of npx hardhat compile as it will run a script to update the src files in the contracts directory of the latest typechain output.

[drewstone]

Awesome work, first glance is # of files / lines changed is huge. Maybe we're committing something we shouldn't be. Phone isn't loading commits easily..

EDIT: Looks like mostly TS type files. I presume we're not using a large majority of them for anything. We should remove and try to shrink the size of these types, isolating them as much as possible if not already done. Wdyt?