Hooked up the start/stop/set-tags functions to the hotkeys. Below are more details of the changes:

- Changed the GlobalHotkey class so that it's not static and it injected via Ninject.
- The HotkeyManager now implements a new interface called IHotKeyRegisterCallback which just has a single method to allow the NotifyIconViewModel to register callbacks to the hotkey actions.
- Moved the Callback property out of the GlobalHotkey class and into it's own class (called Hotkey) together with the action state (new HotkeyActionEnum). It shouldn't really have been in the low level GlobalHotkey class.

This is now ready to merge into the develop branch. The only think left for hotkeys is to add the configuration UI to the options dialog.