Reactor timers from NSTimer to GCD Source.timer

This PR moves the Reactor Timers from NSTimer to GCD Source.timer, this will also fix #240. to addition to that, we don't have to care about __Run Loop Modes__ any longer \o/.
At the moment the Timer is executed in the Current **Dispatch::Queue**, but if need we can pass a queue as an option in which the timer can/could be executed.

your feedback is highly appreciated!