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.

Tactility/Source/service/gui/Gui.h

@@ -1,7 +1,7 @@
 #pragma once
 
+#include "app/AppInstance.h"
 #include "app/AppContext.h"
-#include "ViewPort.h"
 
 namespace tt::service::gui {
 
@@ -10,10 +10,8 @@ typedef struct Gui Gui;
 /**
  * Set the app viewport in the gui state and request the gui to draw it.
  * @param[in] app
- * @param[in] onShow
- * @param[in] onHide
  */
-void showApp(app::AppContext& app, ViewPortShowCallback onShow, ViewPortHideCallback onHide);
+void showApp(std::shared_ptr<app::AppContext> app);
 
 /**
  * Hide the current app's viewport.