Resource policy support for QSoundEffect.

Since sound effects are something short and mixed with other audio, do
not acquire resources explicitly. Follow the resources availability
information to determine when it is ok to play the sound effects.

When client has registered itself to resource manager, client's streams
are classified properly. If no higher priority client has acquired the
resources, isAvailable() is true, and sound effects can be played. We
do not explicitly acquire the resources, since then other clients with
the same resource class would lose the resources, thus not possible to
have second client play music with QMediaPlayer class while our client
would just want to play simple sound effects.

Change-Id: Ib5589349dca6900a8bee616b8ad77e7cb5ec9533
Done-with: Juho Hämäläinen <juho.hamalainen@tieto.com>
Reviewed-by: Andrew den Exter <andrew.den.exter@qinetic.com.au>