EMI: various costume and sound fixes

I created this patch series when I tried to get the sound of the paddles in the swamp working.

I'm not 100% sure about these patches so I'm looking forward for your comments!

It fixes:
1. costume was not found for raft
- if costume can't be found, try to load it using pushCostume()

2. isPlaying() function for various track implementations

3. don't start playing a sound if it is already playing
- the lua calls from the chores engines/grim/emi/costume/emiluavar_component.cpp are so fast, that usually the sound is still playing
- due to the implementation of the mixer, it is not possible to stop both sounds - so don't do it

4. on some sets a looping sound is kept running because it is not stopped via lua calls when leaving the set
- better stop all pool sounds when changing the set