* bookmark operators: add and delete bookmark
* first start at menus in file browser: Directory and Bookmarks
* Adding a bookmark via menu or via CTRL+B
* Remove a bookmark with the X button next to it.
* start of filebrowser RNA
* system files, bookmarks, etc. now nicely inside panels to allow collapsing etc.
* filebrowser header now defined in space_filebrowser.py
TODO:
* button type for bookmarks etc. not final yet, at least should get centered still. Suggestions welcome here.