Added initial sound support

- Add sound component to entity to make it play a sound.

- If sound is large, streams via Gdx.audio.music;
if small, loads in-memory via Gdx.audio.sound.
No difference in usage (except less precise isFinished() if small).

- Volume updated via _effects_volume float variable, as modified by
component volume (defaults to x 1.0).

- Cleanup ensured in reset() method, once sound is over.
Gdx.audio.sounds assumed to be up to 2s long.
Added demonstrator to cooldemo.

- change language to spanish to hear "the rain in spain",
a long fragment loaded via Gdx.audio.music

- change language to english to hear a blip,
a short fragment loaded via Gdx.audio.sound

- change bee transparency to alter volume.
Fixed insidious bug due to cached sound instances
Merge pull request #593 from manuel-freire/initial-sound-support

Initial sound support