Added possibility to setup alliances in the lobby
fixes #310

The available team ids that a seat can use are defined in the level file
Note that the order matters as the first one in the list will be selected by default.
With this logic, some seats can be sealed while others can be setup in the same level.
Examples to test are used in multiplayer small test map FFA and skirmish 2v2 small test map.
Workers with claimrate = 0 should not try to claim. Same for digging.
fixes #308
Merge pull request #321 from Bertram25/boulder

Some quick-fixes
Merge pull request #319 from hwoarangmy/development

Added possibility to setup alliances in the lobby + workers with claimrate = 0 do not claim anymore
Added support to make an entity translucent, and used it to show when a boulder trap is deactivated.

Fixes #294