Add highlighted images to doors so they "glow" when approached

[dylanm312]

Is your feature request related to a problem? Please describe.
In general, interactive objects in Gather "glow" with a yellow/gold halo when the user approaches them, to signal their interactivity to the user. This is done on Gather's end by swapping the "normal" object image for the "highlighted" object image (and then back again when the user recedes.)

(Above, the AMS sign glows when a user approaches it.)

At the moment, doors created with this tool don't "glow" when approached, so the only indication of their interactive nature is the "Press X to interact" message at the bottom of the screen.

Describe the solution you'd like
Adding new fields to the Door objects for a highlighted "closed" image - and then adding that image to the object in gather_door_updater.py - would allow for doors to glow when approached, improving the overall user experience. Note that the "glowing" image would have to be manually created in Photoshop or another image editing tool. As far as I know, there is no built-in method for making things glow in Gather (although that would be cool).

Describe alternatives you've considered
The alternative would be to leave it as-is, with the doors not glowing. This works, but isn't particularly intuitive for the user.