Drag and Drop Basics - Githubissues

To test this PR the Dock should be able to do the following:

Load NSUserDefaults values
If NSUserDefaults is an empty array, load Terminal and SystemPreferences
Dragging a docked group icon that is not running out of the docked window will remove it from the dock
Dragging a running docked group icon out of the docked window will add it to the running group
Adding running group icons to the docked group can be done by dragging it over
Any changes to the docked group should automatically update the stored defaults

I think that is everything for this PR.

gershwin-os / dock