cleanup, timermanager in App is a dependency that takes timers again.

App now adds already constructed Timers
Timer is now an Invoker that takes a weak_ptr to a steppable with a
request()rather than a bool callback.
should eventually be changed to composition

src/steppable.hpp

@@ -8,7 +8,7 @@ public:
 	virtual ~Steppable() = default;
 	bool is_finished = 0;
 	size_t stepcount = 0;
-	virtual bool step() = 0;
+	virtual void step() = 0;
 };
 
 #endif