Add M320 as a UGL

M320 with stock attached can be disassembled into stock and M320 GLM.
The GLM can be attached to rifles or used as a craft component alongside
the stock in making the stand-alone launcher.
elusive
cougar spawn
No more Zombear swarming.
Merge pull request #6987 from dar-/m320-underbarrel

Add M320 as a underslung grenade launcher
Merge pull request #7026 from Wishbringer/ZombearTweak

Spawn Zombears less often early in the game.
Merge pull request #7024 from Lain-/elusive-cougar

Elusive cougars