ColorSetting implementation described in issue #292
Replaced AC & BG options with ColorSettings.
Added ColorSetting with click-to-edit color preview button. No lock(), isLocked() and setCheckedIgnoreLock() functions were implemented yet. Alpha channel selection is not implemented for now (may be in future pull request).
Added EditColorScreen with RGB input fields and clickable color palette. After changes applied the setting is saved in json as string in RGB CSV format (example: "255,128,0").
Added basic .setcolor cmd (untested by me yet, including CheckboxSetting.getPossibleKeybinds())