Refactor app launching (#174)

- Refactor the way apps work: Instead of a C interface, they are now C++ classes. The main reasoning is that attaching data to an app was cumbersome. Having different implementations for different kinds of apps was cumbersome too. (3 or 4 layers of manifest nesting for the TactilityC project)
- External apps are still written in C, but they get a createData/destroyData in their manifest, so:
- External apps now have their own manifest.
- All functions in the original AppManifest are removed and replaced by a single `createApp` function
- External apps now automatically register (each app individually!) when they run the first time. As a side-effect they become visible in the `AppList` app!
- Adapted all apps for the new interface.
- Adapted all internal logic for these changes (Gui, ViewPort, Loader, AppContext, AppInstance, etc.)
- Rewrote parts of Loader to use std::shared_ptr to make the code much safer.
- Added a refcount check for the `AppInstance` and `App` at the end of their lifecycle. Show warning if refcount is too high.

TactilityC/Source/tt_app_context.h

@@ -11,14 +11,6 @@ typedef void* AppContextHandle;
 /** @return the data that was attached to this app context */
 void* _Nullable tt_app_context_get_data(AppContextHandle handle);
 
-/**
- * Attach data to an application context.
- * Don't forget to manually delete allocated memory when onStopped() is called.
- * @param[in] handle the app context handle
- * @param[in] data the data to attach
- */
-void tt_app_context_set_data(AppContextHandle handle, void* _Nullable data);
-
 /** @return the bundle that belongs to this application, or null */
 BundleHandle _Nullable tt_app_context_get_parameters(AppContextHandle handle);