[rbp/omxplayer] Handle displaytime more like dvdplayer

We had various glitches when mixing seeking and trickplay with online streams or dvd content.
This tries to match more closely what dvdplayer does and fixes some seek/trickplay jumping issues
[rbp/omxplayer] Avoid loss of volume messages

There seems to be a race condition where the volume request arrives as the omx audio pipeline is being created.
Restructure the volume messages to apply the initial volume as pipeline is being created, and add missing locks.
This also reduces the differences between OMXPlayer and DVDPlayer
Fix for broken build: do not cast n_BufferCountMin to unsigned integer [rbp]
VideoRenerers: add buffering
add buffering for GLES
WinRenderer: add buffering
DXVA: activate buffering in renderer
linuxrenderer: delete all textures on reconfigure
drop frame counter in application, ask render manager instead
vaapi: adopt to buffering in renderer
add buffering - some documentation
RenderManager: only flip free buffer if player has added something
move NUM_BUFFERS up to BaseRenderer.h
OverlayRenderer: align buffers with index in renderManager
add buffering - submit absolute time to render buffers
RenderManager: some rework, squash add buffering
dvdplayer: disable buffering unil dropping is improved
RenderManager: skip very late frames in render buffer
renderbuffers: drop enable/disable in this iteration
RenderManager: add method SetSpeed