Merge pending-release into master

To be merged right before the 0.8.6 release.
Do NOT squash commits, it is important to preserve the history.

The pending-release branch contains map changes that affect the gameplay and would lead to glitches/other quirks for 0.8.5 clients playing on autobuild/git servers (or vice-versa) if these changes were merged to master directly.

Map changes that were merged in the pending-release branch:

• !43 (merged): Add the map Go by dublpaws and Debugger.
• !161 (merged): Remove Drain and Oilrig.
• !162 (merged): (Stormkeep) Fix a wallwalk to the MH (by moving a brush 0.125 qu).
• !163 (merged): (Implosion) Add flare lights on top of the radio pylons + clip the wall details in the corridors + brush cleanups + texture fixes.
• !166 (merged): (Atelier) Slightly raise the teleporter exits and make the decals underneath non-solid.
• !169 (merged): Add the map Trident by proraide.
• !178 (merged): Update the campaign with new maps and new game modes.

Fixes: #204 (closed)