First steps to achieve undo tab closing: add menu items, a hotkey and other resources

GUI: New options are seen in the File menu ("Undo Close Tab"), after right-
clicking on a tab ("Undo Close Tab" is also seen) and, as in Dolphin, in
the Go menu ("Recently Closed Tabs") so the user can choose which tab to
restore (not only the last closed one) or choose "Empty Recently Closed Tabs".

Revision: !49