Refactor app access (#205)

- Use `tt::app::` functions to start/stop apps and get current app(context) instead of using loader everywhere
- Removed `tt_service_loader.*` from TactilityC
- Created `tt_app_stop()` for TactilityC
- Bumped version to 0.3.0 to prepare for upcoming release

TactilityC/Include/tt_app.h

@@ -29,6 +29,9 @@ bool tt_app_has_result(AppHandle handle);
  */
 void tt_app_start(const char* appId);
 
+/** Stop the currently running app */
+void tt_app_stop();
+
 /**
  * Start an app by id and bundle.
  * @param[in] appId the app manifest id