GUIEpgGridContainer: validate scroll offsets as well as they are used to calculate rendered blocks
GUIEpgGridContainer: don't select first item on mouse/touch event on empty programme block
GUIEpgGridContainer: don't react on clicking channel list
GUIEpgGridContainer: add panning gesture
GUIControlGroupList: add panning gesture
Merge pull request #2587 from pieh/panning

Add gesture handling to GUIControlGroupList and GUIEpgGridContainer