PPageFileInfoRes: Various cosmetics.

Reduce the visibility of the member functions and variables and simply the code.
Property dialog: Decide whether to show the "Resources" tab without checking the graph twice.
Property dialog: Ensure the focus stays consistent when switching to the "Resources" tab.

Previously the file name could get highlighted.
Property dialog: Make the UI more consistent between the tabs.

The header was slightly different on the "Resources" tab.
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...