[pvr] use ACTION_PREVIOUS_MENU to access the menu sidebar

As already discussed in the forum, this improves the usability to access the menu sidebar while in EPG grid and all PVR related windows. Currently if you stay in epg grid it's only possible to reach the sidebar if you move to left/right end of the epg grid. So this adds the use of the action ACTION_PREVIOUS_MENU to quickly access the sidebar.