Revised Forcefield Sounds addon - Half-Life 2

It's always kinda bothered me that the Combine forcefields use the same footstep noises as concrete, so I made a quick little addon to rectify that. Included is a modified version of the hard_light_bridge surface property and appropriate sounds from Portal 2, and and new materials so the Combine forcefield textures to use that instead of the default. It's especially noticeable in the Episode 1 Citadel levels, but it might come up in other areas.