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/Private/app/wificonnect/WifiConnectPrivate.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "app/App.h"
 #include "app/wificonnect/Bindings.h"
 #include "app/wificonnect/State.h"
 #include "app/wificonnect/View.h"
@@ -9,7 +10,10 @@
 
 namespace tt::app::wificonnect {
 
-class WifiConnect {
+class WifiConnect : public App {
+
+private:
+
     Mutex mutex;
     State state;
     Bindings bindings = {
@@ -28,8 +32,8 @@ public:
     void lock();
     void unlock();
 
-    void onShow(AppContext& app, lv_obj_t* parent);
-    void onHide(AppContext& app);
+    void onShow(AppContext& app, lv_obj_t* parent) override;
+    void onHide(AppContext& app) override;
 
     State& getState() { return state; }
     Bindings& getBindings() { return bindings; }