utils: add expandpath() function

We'll reuse it when reworking the bookmarks widget.

Signed-off-by: David Aguilar <davvid@gmail.com>
bookmarks: defer loading settings until after the GUI is initialized

Signed-off-by: David Aguilar <davvid@gmail.com>
bookmarks: get rid of the bookmarks dialog

Move the Add and Delete functionality into the bookmarks widget itself
so that we eliminate the separate dialog.

We still list recent repositories in the list, but it's easy to remove
them now.

Closes #289

Suggested-by: 字龍(Vdragon) <Vdragon.Taiwan@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>