Fixed issue where door would close after a few seconds.

Small visual update:

- Changed the lightmap scale on a few surfaces to better match the rest of the chamber
- Added lights to signage
- Added some floor detail so the first switch is more noticeable
- Replaced the stock Portal 1 doors with Valla-Chan's P2 styled remake of the P1 doors

Didn't want to change up too much, since that'd defeat what I was going for with this map, but I felt it could use some touching up now that a better P1 door model exists.