bump minimum supported Android version to 14 aka 4.0 aka Ice Cream Sandwich

Android 4.0 aka android-14 was released on October 18, 2011, so a long time ago. android-10 had a lot of users, but 11-13 (Honeycomb) had very few. By moving to android-14 we can:

• Android support libs >=26.0 require android-14
• purge lots of special cases in the code to support only android-10.
• switch our unmaintained PreferenceFragment to the official PreferenceFragment
• ditch partially maintained SpongyCastle (its missing com.madgag.spongycastle:pkix) and use the official BouncyCastle releases.
• ditch our unmaintained fork of BottomNavigation since upstream does not want to support < 14
• use Uri.getQueryParameterNames() for swap URLs

By switching to android-16, we can:

• ditch jmdns and use the built-in NsdManager

By switching to android-18, we can:

• use SHA-256 in the APK signatures
• purge lots of special cases in the code to support older than android-18.

Here is the count of Build.VERSION.SDK_INT tests in the code:

• android-10: 1
• android-11: 10
• android-13: 1
• android-14: 9
• android-15: 2
• android-16: 10
• android-17: 2
• android-18: 8