Enhance BACK button (KEY_LAST) to free up PREV and NEXT buttons for time shifting

[IanSav]

During discussions in the forum a few button rearrangements have been discussed. There is a desire to remove the "History zap" screen function from the PREV and NEXT buttons in live TV mode so that those buttons can consistently be used to navigate the time shift buffers. (At the moment PREV and NEXT only navigate the time shift buffers when actually time shifting.)

To keep access to the "History zap" screen it is proposed to enhance the functionality of the BACK button. BACK should be configurable via a configuration option to select if it immediately executes the zap (as it does now) or brings up the "History zap" screen (the proposed enhancement). To make the most of this functionality and capitalise on the available long press option a long press BACK should automatically assume the role of the opposite option selected for the short press.

If this enhancement is actioned then we won't need the undocumented KEY_BACK function code that directly accesses the "History zap" screen.

Once the PREV and NEXT buttons are freed up then they can be assigned to step backwards and forwards, respectively, through any available time shift buffers. By implication the PREV and NEXT buttons will be an additional method for entering time shift playback.