All mechs get a melee attack

* All mechs have a melee attack now not just combat mechs, but the force of non combat mechs is only 5. Should fixes #5618 .
* Changing the mech melee attack code to be more object oriented. Creating mech_melee_attack() proc for atom and overidden in its children.
* Mechs can now hit windoors with their melee attack. (they can still open them by bumping)
* Fixing Typos here and there.