Cosmetics: Avoid shadowing variables by using better names.

Additionally use AppendFormat when possible.
Add a "Copy to clipboard" feature to the "Play > Filters" menu.

The list of filters is quite useful for debugging purpose.
Why "C:\tmp.srt"?
Fix some CPPCheck warnings or mark them as intentional.
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.