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/AppContext.h

@@ -1,12 +1,15 @@
 #pragma once
 
-#include "AppManifest.h"
 #include "Bundle.h"
 #include <memory>
 
 namespace tt::app {
 
+// Forward declarations
+class App;
 class Paths;
+struct AppManifest;
+enum class Result;
 
 typedef union {
     struct {
@@ -28,14 +31,10 @@ protected:
 public:
 
     virtual const AppManifest& getManifest() const = 0;
-    virtual std::shared_ptr<void> _Nullable getData() const = 0;
-    virtual void setData(std::shared_ptr<void> data) = 0;
     virtual std::shared_ptr<const Bundle> getParameters() const = 0;
-    virtual Flags getFlags() const = 0;
-    virtual void setResult(Result result) = 0;
-    virtual void setResult(Result result, std::shared_ptr<const Bundle> bundle)= 0;
-    virtual bool hasResult() const = 0;
     virtual std::unique_ptr<Paths> getPaths() const = 0;
+
+    virtual std::shared_ptr<App> getApp() const = 0;
 };
 
 class Paths {