Separate the welder into its own weapon

[ZdrytchX]

Issue: 1. Welder takes up axe slot
Bug: Ejecting the welder in primary slot does not give axe back
Bug: Having no weapons makes weird shit happen
Issue 2: Make the Builder do all the building when pressing E like old ns2
Issue 3: Builder should be a selectable weapon

Far Future:
Issue 4: Builder should be able to build its own structures without the need for the commander. Command station can just be a simple thing that drops ammo and does research