Branch/tdg units

@eric79 @youngca 
Here's the first pass of getting unit icons so that they can be added to the map.
The YAGNI principle would suggest to leave these functions out until they are needed for something.  That way they won't clutter the file, adding noise that a reader has to sift through to find the real stuff.  Eventually, leaving these functions out will be a good thing because if they don't exist, the kernel will automatically call `satProperty` in their stead.  For now ... do you want to call `satProperty` from inside them?