* PLT-3695 unitying upgrade support
* PLT-3695 refactoring to use sql_upgrader
* Fixing unit test
* Adding 3.3 to 3.4
* Fixing upgrading
* Seperating DB schema from version.go
* Fixing upgrade cmd
* Moving to const for exit codes
* remving old unused code
* Added model objects for emoji
* Added database tables for emoji
* Added settings for custom emoji
* Added serverside APIs and unit tests for custom emoji
* Added additional validation to catch duplicate emoji names earlier on
* Added additional validation to prevent users from adding emoji as another user