add AudioManager with device and driver list methods
add AudioManager constructors
integrate AudioManager into engine
audio: add opus loader and basic audio manager
Merge branch 'master' into audio

Conflicts:
	src/CMakeLists.txt
audio: add some comments
ci: add opusfile dependency to .travis.yml
Merge branch 'convertdat' into audio
audio: add resource loading via sound_file vector
audio: integrate Sound class into AudioManager
Merge branch 'master' into audio
audio: read sound_file data from csv
Merge branch 'master' into audio

Conflicts:
	src/CMakeLists.txt
audio: integrate audio ingame
audio: improve sound interface
Merge branch 'audio'