Click on selection column header in group view, will switch between:
 - install all packages in group (not already install)
 - remove all packages already installed in group
 - back to initial selection

Click on selection column header in package view (updates only)
will switch between:
 - select all updates.
 - deselect all updates.
 - back to initial selection

Added '--exit' command line option to exit session based dbus services started
by a yumex (Status icon & YumReadonlyBackend)
Start yumex when user click status icon and there is available updates
change the search entry so it only does auto search when searching only in package
names, when searching a wider scope, then first do the search when return is pressed.