Firebase emulator testing (#9)

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

firebase.json

@@ -0,0 +1,23 @@
+{
+  "emulators": {
+    "auth": {
+      "port": 9099
+    },
+    "database": {
+      "port": 9000
+    },
+    "storage": {
+      "port": 9199
+    },
+    "ui": {
+      "enabled": true
+    },
+    "singleProjectMode": true
+  },
+  "database": {
+    "rules": "database.rules.json"
+  },
+  "storage": {
+    "rules": "storage.rules"
+  }
+}