improv(GUI FileChoosers and file/folder opening): Open filechoosers in center of SPC window. Centralize file and folder opening to utilities.

improv(GUI status display): Display a scrolling bar during the generation of a server pack to indicate that ServerPackCreator is currently doing something. Thanks to @Kreezxil for the suggestion!

improv(GUI Ready status): Enable generation button and turn of status bar after generation has completed, but before dialogs are shown. Looks better and makes more sense.