Store cover tile per player per surface per force

[Stringweasel]

Created as suggested by Lou: viewtopic.php?p=674091#p674091

Currently the default cover tile that's used for force building is stored per force, and not per player. This can create very annoying situations in multiplayer where while you're purpousfully using a specific cover tile, and someone else places a different cover tile, and suddenly any new entities you place uses the other cover tile.

This can get especially frustrating in modded instances too where there are big differences between the different cover tiles. For example in Space Exploration where the empty space tile is not buildable. You could place some form of scaffoling tile on it to build, or a spaceship tile. And there are big differences to the costs and impact of these tiles, and it seemingly randomly changing while building is not a great player experience.

Edit: I know it's techically also stored per tile, but that made the thread title too long. And doesn't change the idea of this request.