dialogue colour

Fixed an issue where dialogue choices were being displayed in the wrong
colours.
3D Audio

Added 3D audio into the game.

The new component SoundEmitterComp provides an interface for objects to
create sounds in 3D space. The comp takes the name of an audio file as a
string and an optional bool for looping sound and nothing more.

The manager for this new comp, SoundEmitterManager, updates the comps
whenever they may have moved (i.e. when the game isn't paused) to ensure
the origin of their sounds is correct. The update process is staggered
(only so many comps will ever be updated in a given frame) to minimize
update time as it isn't essential that sound origins be absolutely
precise and a level may contain a large number of SoundEmitterComp
objects.

The scene .xml file now holds an element "audio" which describes the
ambient  audio for the given level; the ambient audio is played on a
continuous loop so long as the level is active, even when the game is
paused.