proguard: don't warn for test classes

// FREEBIE

proguard.cfg

@@ -1,5 +1,12 @@
 -dontobfuscate
 
+## Tests
+-dontwarn org.mockito.**
+-dontwarn org.fest.**
+-dontwarn sun.reflect.**
+-dontwarn android.test.**
+-dontwarn org.thoughtcrime.securesms.**.*Test
+
 ## Support
 
 -keep class android.support.v4.app.** { *; }