1.2.0 release

- Migrate to JSON i18n
- Remove wfMsg / wfMsgForContent usage
- Raise minimum MW version to 1.20
- Unstrip strip items of 'general' category
- Swap SpecialVersionExtensionTypes for ExtensionTypes

@note: ~1.2 is equivalent to >=1.2,< 2.0

Change-Id: Iacc18361d93f7fb9d29efd49cba11bf897ce6e8c