Make Crashlytics optional

app/build.gradle

@@ -84,6 +84,11 @@ android {
             minifyEnabled true
             zipAlignEnabled true
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
+            ext.enableCrashlytics = file("fabric.properties").exists()
+        }
+
+        debug {
+            ext.enableCrashlytics = false
         }
     }