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/app/ManifestRegistry.h

@@ -1,21 +1,23 @@
 #pragma once
 
-#include "AppManifest.h"
+#include "App.h"
 #include <string>
 #include <vector>
 
 namespace tt::app {
 
+struct AppManifest;
+
 /** Register an application with its manifest */
-void addApp(const AppManifest* manifest);
+void addApp(const AppManifest& manifest);
 
 /** Find an application manifest by its id
  * @param[in] id the manifest id
  * @return the application manifest if it was found
  */
-const AppManifest _Nullable* findAppById(const std::string& id);
+_Nullable std::shared_ptr<AppManifest> findAppById(const std::string& id);
 
 /** @return a list of all registered apps. This includes user and system apps. */
-std::vector<const AppManifest*> getApps();
+std::vector<std::shared_ptr<AppManifest>> getApps();
 
 } // namespace