Added config, raid check and random difficulty chance loot conditions

[flowerfugue]

Finally got around to doing this! The config loot condition was just added because i realised the 'normal' condition type isn't compatible with loot tables, and the random difficulty and raid conditions should be generally useful in the future. I'm also going to need them to convert some hardcoded loot table stuff into fully data-driven modifiers in S&R once those are done :P

I'm still a bit iffy about the documentation, so tell me if you see anything wrong with that.

[flowerfugue]

when the import is unused! 😳