Migrate functional key layouts to json (#778)

Now the functional key layouts should be (mostly) compatible to FlorisBoard
Not yet customizable, this is a large step towards customizable functional key layouts

app/src/main/java/helium314/keyboard/latin/settings/Settings.java

@@ -706,4 +706,7 @@ public final class Settings implements SharedPreferences.OnSharedPreferenceChang
         return wrapper;
     }
 
+    public boolean isTablet() {
+        return mContext.getResources().getInteger(R.integer.config_screen_metrics) >= 3;
+    }
 }