[pvr] adjust labels for setting pvrplayback.startlast

This change the current used labels 'Yes' and 'Minimised' to 'Foreground' and 'Background', so it's easier to understand what's happen if you choose one of these options.
[pvr] remove unnecessary filler method for setting 'pvrplayback.startlast'

This removes the filler method for setting 'pvrplayback.startlast' and add options directly to the settings.xml.
[pvr] refactor: change method parameter bPreview to bMinimised to be more reasonable
[pvr] refactor enum ChannelStartLast to reflect the setting
Merge pull request #4969 from xhaggi/pvr-refactor-setting-pvrplayback-startlast

[pvr] adjust labels and refactoring for setting 'pvrplayback.startlast'
videoplayer: adapt lateness detection and dropping to buffering
video player: present correct pts to user for a/v sync (after buffering in renderer)
videoplayer: some rework and documentation
renderer: bump buffers to 5
videoplayer: update frametime, it might change due to fps detection
videoplayer: give streams with invalid fps a chance for fps detection
dvdplayer: allow rewinding at end of stream, do a seek after rewind
dvdplayer: observe pts counter overflow
dvdplayer: avoid short screen flicker caused by unnecessary reconfigure of renderer
vdpau: advanced settings for auto deinterlacing
player: fix rewind
OMXPlayer: some caching fixes for pvr
fix incorrect display of fps when dr kicks in
ActiveAE: slightly reduce buffer size
Revert "vdpau: comment some features that will be added later"

This reverts commit e00b4f65864d623ab4d2e9e5c06db138e661f1cf.