Move ProGuard rules for Briar to briar-android.

bramble-android/proguard-rules.txt

--keep,includedescriptorclasses class org.briarproject.briar.android.**,org.briarproject.briar.api.android.** { *; }
-
 # Keep the H2 classes that are loaded via reflection
 -keep class org.h2.Driver { *; }
 -keep class org.h2.engine.Engine { *; }

briar-android/proguard-rules.txt

@@ -3,6 +3,8 @@
 -dontobfuscate
 -keepattributes SourceFile, LineNumberTable, *Annotation*, Signature, InnerClasses, EnclosingMethod
 
+-keep,includedescriptorclasses class org.briarproject.briar.android.**,org.briarproject.briar.api.android.** { *; }
+
 # QR codes
 -keep class com.google.zxing.Result
 -keepclassmembers enum * {