No need to try rebuilding the capture graph when not in capture mode.

Note that this is cosmetic only thanks to another safety check.
EditListEditor: Various cosmetics.

Reduce the visibility of member variables, mark some functions const and other minor cosmetic changes.
Capture dialog: Various cosmetics.

Reduce the visibility of member variables, mark some functions const, use clearer function names and other minor cosmetic changes.
Navigation bar: Ensure the child dialog components are updated.
RTS: Allow to put subtitles higher than video frame with override
placement and subtitles placed relative to video frame.
Increase limit on subtitles override placement feature.

Fixes #2834
Don't force any background color for the Shockwave graph.

This commit fixes #1747.
Why "C:\tmp.srt"?
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...