PerPixelMultiMap with Emissive map 1

Adds a 5th slot, txEmissive, to ksPerPixelMultiMap, that's multiplied by the ksEmissive setting. Lets you go from this to this:

(artist's conception, not representative of the actual parts of the taillights that are brake-related)

To install, extract system+sdk folders into your AC installation, does not overwrite anything.
To use, select ksPerPixelMultiMap_emissive in ksEditor. Paint your new emissive texture with the brightness and colour of light you want from it. Full white = original emission.
To redistribute, include the system folder with your mod.

Potential uses:
running lights (as above)
buildings on a single material with just the windows lighting up, not the entire texture
windows lighting up various amounts across a building, instead of all identical
backlit advertisements that don't light the entire thing uniformly