Timer now contains an invoker instead of inheriting

the idea is that an invoker holds a weak_ptr to a steppable. and
anything with an invoker can advance a steppable

app::add_sort has become too heavy because of the way timer and
invoker are initialized now.

src/sortui.cpp

@@ -30,14 +30,12 @@ int main() {
 
 	auto myviewsession = make_unique<ViewSession>();
 	auto mytimermanager = make_unique<TimerManager>();
-	
+
 	//create app with initialized dependencies
 	App myapp(std::move(myviewsession),std::move(mytimermanager));
 
 	//add and connect data
-	Timer timer(0, chrono::milliseconds(250));
-	myapp.timermanager->timers.push_back(timer);
-	myapp.add_sort(myinput, "bsort", myapp.timermanager->timers.back());
+	myapp.add_sort(myinput, "bsort");
 
 	//actually start the app
 	myapp.run();