TokenBridge Contracts 6.0.0

Merge the develop branch to the master branch, preparation to v6.0.0

This update for the `master` branch contains the changes made to address findings discovered during a security audit:
 * [Fix] Stricter preconditions for payInterest (#623)
 * [Fix] Fix offset in comments (#624)
 * [Fix] Use fixed lower call gas limit (#627)
 * [Fix] Separate XDaiForeignBridge contract with compound and GSN support (#626)
 * [Fix] Update GSN interface (#628)
 * [Fix] Block ERC20 selectors in AMB requests (#630)
 * [Other] Bump package and contracts interfaces version prior to 6.0.0 (#629)

TokenBridge Contracts 6.0.0-rc1

Merge the develop branch to the master branch, preparation to v6.0.0-rc1

This set of changes includes the following improvements and fixes:
  * [Improvement] EIP2612 permit (#618)
  * [Fix] Make _sendMessage internal (#613)
  * [Other] Fix coverage (#606)
  * [Other] Remove unused upgrade dir (#339 
  * [Other] Bump package version before 6.0.0-rc1 (#619)

TokenBridge Contracts 6.0.0-rc0

Merge the develop branch to the master branch, preparation to v6.0.0-rc0

This set of changes includes the following improvements and fixes:
  * [Improvement] AMB Home-to-Foreign async calls (#570), closes #492
  * [Improvement] Add GSN support for erc20-to-native bridge mode (#571)
  * [Fix] Fix issues with packages versions and linter (#600)
  * [Other] Bump package version before 6.0.0-rc0 (#598)

TokenBridge Contracts 5.7.0-rc1

Merge the develop branch to the master branch, preparation to v5.7.0-rc1

This set of changes includes the following improvements and few fixes:
  * [Improvement] Earn interest on locked tokens using Compound Protocol (#590)
  * [Other] Remove deprecated bridge types (#595)
  * [Other] Bump contracts and package version before 5.7.0-rc1 (#597)

TokenBridge Contracts 5.7.0-rc0

Merge the develop branch to the master branch, preparation to v5.7.0-rc0

TokenBridge Contracts 5.6.0

Merge the develop branch to the master branch, preparation to v5.6.0

TokenBridge Contracts 5.6.0-rc0

Merge the develop branch to the master branch, preparation to v5.6.0-rc0

TokenBridge Contracts 5.5.0

Merge the develop branch to the master branch, preparation to v5.5.0

TokenBridge Contracts 5.5.0-rc0

Merge the develop branch to the master branch, preparation to v5.5.0-rc0

TokenBridge Contracts 5.4.1

Merge the develop branch to the master branch, preparation to v5.4.1