Purchases should be cached for use without an internet connection

[jambl3r]

Developer TODO (don't remove)

• update documentation

Every time the app opens it checks the internet to see what the user has purchased. If there is no connection, all features are blocked.

Additionally there can be strings like "You must purchase floating buttons" which is confusing to people who have already bought it #1649

The app should cache purchases for a set period for use without access to the internet.