[keyboard layouts] use English language names

Also added small comment to guide future contributors.
Merge pull request #5525 from uNiversaI/keyboard

[keyboard layouts] use English language names
videoplayer: adapt lateness detection and dropping to buffering
video player: present correct pts to user for a/v sync (after buffering in renderer)
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
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.
xbmc pr 3080
ActiveAE: add some debug logging
dvdplayer: rename codec ctrl flags
VAAPI: implement codec control flags
consider rounding errors in dropping control
pthreads: use mutex protocol PTHREAD_PRIO_INHERIT