At least we can now see the difference between loop1 and loop-all

close #3343

This is an arbitrary choice. But KiB are much more common than kB.
Also the notation is unambiguous.

Note that we keep kbps for *bit* rates.

Fix #3349.
Unfortunately we can not use QStyle to handle selection generically across platforms.

 It was incomplete and was creating issues when the audio output provided a
non mono device (close #3272).

Use of function references rather than function names to store button
actions. This allows using all kinds of functions, including non global
ones. Note that the old mechanism using global function names is not
supported anymore. Existing scripts will need to be fixed (-> just
remove the quotes around the function name).

Change vlc.stream() and vlc.memory_stream() error reporting to behave like lua's io.open() or loadfile() functions.

Close #3368

Ref #3368

This reverts commit d69b5e60.