[GEM Management] Add a function to activate / desactivate Gem (Skill / Spirit)

Hi,

Right now it is kind of boring to change Gem between Mapping / Bosses.

Adding more socket for Gem but with a new function to activate / desactivate a Gem (for both Skill and Spirit Gem), and put the limit on this function instead.

I don't know if it has already been reported before, but I'm pretty sure to not be the only one in this case.