Increase min android version

[CodeDoctorDE]

Starting with Butterfly 2.3.0-beta.1, the minSdkVersion gets increased from 21 to 23 since dependencies I depend on needs this. This means, you need Android Marshmallow (Android 6) or higher to run the app. Android 5 was released 2014, 10 years ago so I recommend everyone to just use a newer android version or if the device manifacture doesn't update the phone anymore, to use a custom rom. The web version should also work fine.
Since play store isn't updated anymore on these devices, google seems to also shutdown the maintainance.

See https://en.wikipedia.org/wiki/Android_version_history for reference.

Butterfly 2.2 should keep supporting Android 5. It will be supported until the big butterfly 2.3 gets out (I'm planning the release in 3 months).