Make SoundManager support playing sound on locations, were distance
from location to pc controls the amplitude, eg. the further away the
sound is the more faint it is played out.

Made Map events on_load special for looping a sound effect at the
position of the event, this will be used for location based env.
effects like the fires we now have in warp zone and atrium.
Rename sfx to soundfx for consistency in data files.

Fixes #388
Merge pull request #389 from hean01/env_sound

Support for location based environmental sound effects.
Merge pull request #390 from hean01/soundfx_attribute

Rename sfx to soundfx for consistency in data files.