Merge Localizable strings

In Element, we currently have 3 localization file schemes:
1) Vector.strings - main application translations
2) MatrixKit.strings - translation migrated from the MatrixKit
3) Localizable.strings - strings used only in the notification extension

We should merge all of them together into Vector and clean up Weblate.
While merging the MatrixKit ones in is rather straight forward for 3) we will need to migrate from the `localizedUserNotificationString` method (which seems to only be useful for scheduled local notifications) to a normal swiftgen template one.