Construct HUD sprites

I'm counting on Ragnasal to take it up from now. Includes health sprites
for all three constructs, as well as shared pull, fire, and zone_sel
sprites.

I don't know how HUD code works yet, reguarding health percentages, so
I've indicated the icons that should correspond to to the various health
levels in the following pics:
https://dl.dropboxusercontent.com/u/33846352/artificer_health.gif
https://dl.dropboxusercontent.com/u/33846352/Wraith_health.gif
https://dl.dropboxusercontent.com/u/33846352/juggernaut_health.gif