Updated LAV Filters to 0.61.2-11-g70ec47a (custom build based on 0.61.2-6-002d1f2)

Important changes:
 - LAV Splitter: Alternate audio support for HLS (ticket #3575)
 - LAV Video: Support VP7 video
 - LAV Video: Use the MediaFondation WMV decoder on Windows 7+ instead of the DMO WMV decoder
 - Updated ffmpeg and libbluray libraries
Fix: Two private interfaces had the same UUID.

Requesting IBDATuner succeeded even if the interface wasn't implemented since it had the same UUID than IGraphBuilderDeadEnd.

Fortunately this had no visible effect thanks to additional checks.
Renderer statistics: Hide an unneeded line when VSync is disabled.
PGS/DVB subtitles: Simplify the code.

Use only 3 classes instead of 4. Will be useful for some future work.
Fix: Changing the zoom level didn't leave fullscreen anymore after 54d1fa7cd5d3cd448c663033a35e756847de6bad.

This commit fixes #4288.
Fix some CPPCheck warnings or mark them as intentional.
Docs: Change the tag numbering of LAV Filters/ffmpeg.

Follow the same principle as the nightly builds numbering now that we use `git describe`.

MPC-HC 1.7.5 was a hotfix release so neither LAV Filters or ffmpeg were updated so we won't have any tag collision.
WebUI: Inform the web interface that no audio stream is available.
WebUI: Make use of new [hasaudio] info.
What the hell was intended here?!

Trying to make some sense of that code. Without much luck so far...
Fix: x86 and x64 versions conflicted over file associations.

4f465cf8b81f1da800b1bfc57cc48e317d24fbb5 was incomplete for Vista+.

This commit fixes #4064.