Missing space
Audio system cleanups

This commit allows for enabling or disabling openal support with USE_OPENAL[0|1] flag. By default, openal is
enabled (and preferred). If no sink is selected, audio will be completely disabled. This also reduces load,
since no work related to audio handling will be done. Audio sink is now written to config file, and can be selected
by changing value there. Also, use add_definitions() function in cmake for adding compiler definitions.