Fix #17: Lock doors when obstructed on either side to help pathfinding

75e89706 adds the previously untracked file Data/Scripts/EnvObjects/Door.lua in unmodified form to help future blames on this file. 227d9f53 adds the real code that fixes this issue.

Please refer to the individual commit messages for more information and refrain from squashing these commits together in order to not obstruct future blames against this file.

Known issues: When a door is locked due to obstruction, it shows that it is locked due to vacuum. Purely cosmetic, might confuse players.