Package Android binaries, enable desugaring, bump min API level.

FIXME: Desugaring ConcurrentHashMap.newKeySet() requires
desugar_jdk_libs version 2, which requires bumping the Android Gradle
plugin version. This seems to have broken Gradle Witness.

bramble-android/proguard-rules.txt

@@ -6,6 +6,9 @@
 -dontwarn org.h2.**
 -dontnote org.h2.**
 
+# Keep sqlite-jdbc-crypt classes that are loaded via reflection or accessed via JNI
+-keep class org.sqlite.** { *; }
+
 -keep class dagger.** { *; }
 -dontwarn dagger.**
 -dontnote dagger.**