- Added $halflambert to all material files
- Added $selfillum to a few material files

Added some models from Half-Life 2: Episodes 1 and 2. Can't recall if anything from Counter-Strike: Source or Day of Defeat: Source was added.

Total model count went from 87 to 131.

All VMTs now have consistent formatting + line endings, for my own sanity.

Lazily made the "Invisible Material" addon a requirement to avoid a missing texture for the keypad on the "door03_left" model from Episode 1. It just makes that third handle bodygroup invisible. I'm too lazy to do actual edits to the models, and sticking with the "no texture files from other games" requirement, this is how things have to be done.

Redid the addon. Fallback models themselves are now from their respective games for compatibility with anything that depends on the proper versions of the models, but their corresponding materials now point to Half-Life 2 textures.
- Added a few Portal 1 fallback models
- Added Day of Defeat: Source fallback models (all furniture + a clay pot)
- Added one Episode 1 fallback model ("static" dumpster, already uses same texture as the "dynamic" dumpster from HL2)
- Consistent VMT formatting.
- Probably some other changes I've forgotten about, it was a bit of a headache to comb through each game's assets and compare each model's data/properties with similar models from Half-Life 2. The only models that are straight up HL2 models are the cargo container and laundry dryer (which is actually the washing machine, but whatever). The rest are just texture/VMT edits.