engine: Generalize console shortcut config values

This patch generalizes configuration names for shortcuts for:
 - releasing cursor from remote-viewer
 - toggling fullscreen in remote-viewer.

The configuration names were originaly intended to be used with SPICE
only, but they are actually valid for VNC as well.

Change-Id: Icd339a326222e3910d835db21ac459540dc74f14
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1083766