Remove "Automatically set speaker count for the ivideo AC3 decoder" option.

The decoder hasn't been updated for years.
About dialog: Add back the FFmpeg compiler in the clipboard output.
DVB: Try to convert language code even if LCID was not found.
Updated German translation.
Updated French translation.
Updated Polish translation.
Disable external subtitles in capture mode.
Revise seek-on-keyframe code

It now uses stl structures and algorithms.
When dragging the seekbar thumb, the thumb now sticks to keyframes
if seek-on-keyframe is enabled.
PlayerSeekbar: handle doubleclick event

To even the numbers of ups and downs.
PlayerSeekbar: remove m_rtPosReal

It just duplicates m_rtPos in current code.
Add fast-seek rounding method selection