I added this in order to debug #2132.
### Changes:
- Extracted `Core` framework to be used by both apps
- Added new `watchOS` target
- Changed `fastlane match` to also create profiles for this new target
- Added a simple view in the watch app that displays a text if an
entitlement is active, or a `restore` purchases button otherwise
This is just a starting point, we can add more to it in the future.
#### Note:
_Unfortunately I haven't been able to test this because of an Apple bug
(`FB11873951`):_
