MediaFormats: RAR was incorrectly flagged as audio-only.

Fixes #3088
update Changelog.txt, thirdparty/versions.txt and release date.
Update Greek translation.

refs PR 76
MP4Splitter: fixed playback for same 3gp with AMR sound (fixed 4496) (ticket #3079)
Audio Switcher: Improve normalization algorithm.

Use a much better regain strategy (similar to ffdshow's) and fix the regain rate to be linear rather than completely exponential.

This commit fixes #1936.
Audio switcher: Use percentage instead of dB for the boost.

Internally a percentage was already used and it is much easier for the user to understand a boost expressed in percentage.
Audio Switcher: Add a setting to change the max normalization factor.

Use a max normalization factor of 4 by default instead of 10 to avoid huge volume variations.

Refs: #1936.
Bump version to 1.6.8.
run astyle
update lcms to 5bf9e43
Auto-load subtitles/audio: Improve multivolume rar file handling

Make it possible to load audio and subtitle files when playing
any .partXX.rar file of a multivolume rar archive:

Assume the following files:
movie.part01.rar
movie.part02.rar
movie.part03.rar
movie.srt
movie.mp3

Playing any of the three .rar files will now auto load the
mp3 and srt files.

Before, the .srt and .mp3 would have needed to be renamed to
something like
movie.part01.srt
movie.part01.mp3