Implemented forge logic

As discussed, the changes are:
- Every created trap is now deactivated by default. It needs a crafted trap from the forge to be activated
- Once activated the trap can shoot immediately
- After a few shoots (configurable per trap in the config files), the trap is deactivated and needs another crafted trap
- Between 2 shoots, there is a reload time
- Attackable traps can be attacked by creatures even when deactivated
- When created, crafted traps use one active spot in the forge until they are taken by a kobold

EDIT:
- I've added support in the level file to choose if a trap is activated or not at load time
- For now, no creature will go on the forge to work by themselves. However, if the randomly go there, they might consider to work. But unlike training hall, they won't go there for that purpose
- For now every creature is as efficient as the others at forge.

Note that the 2 last points will be fixed when #354 will be done