TokenBridge Contracts 3.2.0

This version of TokenBridge supports operations in four modes:

• native coin to an bridgeable ERC20 token;
• an ERC20 token to a bridgeable ERC20 token;
• an ERC20 token to a native coin;
• relaying arbitrary messages (Arbitrary Message Bridging, AMB).

This release contains new two features:

• "Alternative receiver". Any contract in one chain will have the ability to send tokens cross-chain to any external address or contract. This feature will benefit owners of multsig wallets - they will be able to exchange Dai to xDai and vice versa.
• "Phase 1 of migration to MCD". This feature is specific for the xDai bridge and related to the planned by MakerDAO migration from Single-Collateral Dai to Multi-Collateral Dai.

The following changes were included in this version:

• Improvement: Remove deployed at block information in mediators contracts (#292)
• Improvement: Use hex-identifiers directly instead of runtime hash calculation (#303)
• Improvement: Simplify mintReward function (#304)
• Improvement: Alternative receiver for TokenBridge transfer operations (#295)
• Improvement: Add method to migrate from SCD to MCD (#311)
• Fix: Documentation typos (#289, #290)
• Fix: setTotalSpentPerDay called twice in AMB-ERC-TO-ERC (#309)
• Fix: Update interfaces version (#314)