refs https://github.com/TryGhost/Toolbox/issues/138
- Having the "ghost" alias only added cognitive load when reading through the test code and didn't provide any additional value. Removed the pattern to keep things simpler and more explicit
refs https://github.com/TryGhost/Team/issues/1070
- stores values of custom theme settings
- will be merged with full settings data parsed from themes for API output
- will be cached and made available for lookup in themes to avoid db roundtrips
- stores type of custom theme settings so we can coerce values and know if the type has changed when syncing
- records will be synced with themes upon activation