Firebase emulator testing (#9)

- Firebase emulator added
 - Update to Espresso tests
 - Updated gradle dependencies for espresso
 - Updated config.yml
 - Updated android gradle version

storage.rules

@@ -0,0 +1,8 @@
+rules_version = '2';
+service firebase.storage {
+  match /b/{bucket}/o {
+    match /{allPaths=**} {
+      allow read, write: if false;
+    }
+  }
+}