* v2-prototype: (45 commits)
Check length before accessing indices, add awaitTransactionSuccess where needed, and rename function
Add back before/after snapshots for each test
Rename Signer to Wallet, rename GAS_ESTIMATE to GAS_LIMIT
Make preSigned and allowedValidators mappings public
Change names of signature types
Fix formatting and tests
Make AssetProxyId last byte of assetData
Add signer to txHash, allow approveValidator to be used with executeTransaction
Update Whitelist
Fix Exchange interface
Increase block gas limit
Use last byte of signature as signature type
Remove TxOrigin signature type, modify whitelist to use Validator signature type
Update Whitelist contract with comments, also require maker to be whitelisted
Fix build
Add example whitelist contract and minimum tests
Add sample whitelist contract
Add TxOrigin signature type and rearrange order of types
Add approveValidator function
Add Validator signature type
...
# Conflicts:
# packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol
# packages/contracts/src/utils/types.ts
# packages/contracts/test/exchange/transactions.ts
# packages/order-utils/src/asset_proxy_utils.ts
