Bugfix for #935. Removing a package containing an opened ccb file will n...

...ot close the tab.

Removed AppDelegate's removedDocumentWithPath from header, private now.
Removal of a resource triggered with global notification REMOVED_RESOURCE. Set key "filepath" of notification object to specifiy removed resource.

Fixes https://github.com/spritebuilder/SpriteBuilder/issues/935.