Scripting FR: Access to missile lock state

Some things I want to do require knowing how many locks a multilock fighter has, as well as the various multilock configuration values of it's weapon. Things like clearing or setting locks in script would also be useful.

While I'm at it knowing and if/what a missile has locked would be good too if it can't be done already, but I think the target value of a missile can do that already. If we can't set that, it'd good to be able to.