Move old changelog entries to Changelog_old.txt.
PPageFileInfoClip: Various cosmetics.

 - Reduce the visibility of member functions and variables.
 - Simplify the initial focus handling.
 - Various clean-ups.
PPageFileInfoDetails: Various cosmetics.

 - Reduce the visibility of member functions and variables.
 - Simplify the initial focus handling.
 - Various clean-ups.
Properties dialog: Make some strings of the "Details" tab translatable.
Properties dialog: Convert the creation time to the local timezone.
Don't force any background color for the Shockwave graph.

This commit fixes #1747.
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...