Added enemy health bar

First, I want to mention that unity deleted some assets from
L_FG_Asstets_Pack_Lite. I'm not sure why. Sorry about that.. add them
back if it's an issue.
2 bugs:
1- if you kill one enemy, you can't see the health of the other enemy
2- if you kill one enemy before having ever damaged the other enemy, you
can't attack him anymore