Fix broken keyboard shortcuts

The actions were not connected to any accel group. Connecting the
actions with poppup menu items has helped and actions started working.

Before adding the poppup menu, the actions were connected to an accel
group in the code. After the poppup menu, the actions were supposed to
be connected with the default accel group by glade.

See commit f8cfd2cf3ba5b9ee03ac84f35f28385fcb959033 for details.

Signed-off-by: Jakub Filak <jfilak@redhat.com>