Hotkey bar

The hotkey bar and the drag&drop functionality from the spell window for it work now. There is a bug in jQuery which breaks the drop functionality when the draggable icons in the spell window are recreated. This happens whenever the spell windows content changes. I will have to find a workaround for this issue somehow. But this can wait until Milestone 9 when this can actually happen while playing.

A problem is that the icons for all spell levels look the same, so they are hard to tell apart in the quickbar. But that's a purely content-sided problem. I can easily change the actions.json on the server to tell the client to show a different icon for each spell level.

Before I close this milestone I want to look into adding tooltips for the spell icons to show some more of the spell information available to the client.