kmix: Various UTF8 encoding fixes.

This ensures that data that can be UTF8 is treated as such.
Another important fix is the use of QString::number() in the stream names.

Using the number is not great in the first place but the mixer ids need
to be unique. The downside of this is that you cannot split the
channels of a stream and expect it to be restored again (it will be
restored after a reboot but only when the stream indexes match up).

Some better plan is needed here.

That said, this should help restore problems with profiles encountered
with locales that need UTF8 encoding which should also hopefully
help the memory leak that results from this.

However, profile support will still be disabled with PulseAudio backend
anyway, so it shouldn't matter much.