* Extract standard token behaviuor to reuse it in other tests
* Add opt in ERC20 migration contract
* Make migration contract not to depend from standard token
* Changes based on feedback
* Improve MigratableERC20 inline documentation
* move behaviors to behaviors directory
* refactor MigratableERC20 into ERC20Migrator
* fix errors
* change expectEvent to support multiple events with same name
* fix tests
* update documentation
* rename MigratableERC20 files to ERC20Migrator
* move to drafts
* test beginMigration
* rename to ERC20Migrator
* missing semicolon (╯°□°）╯︵ ┻━┻
* add non-zero check
* improve documentation based on review comments
* improve test descriptions
* improve docs
* add getters
* fix contract
* improve tests
