Adding material no_prep properties

[zNightlord]

This is a part of #440 splitted into many PRs.
This first introduce MCPREP_NO_PREP properties under material, this is useful for material doesn't want MCprep prep material overwrites it like on some rigs have been defined in the json file "mob_skip_prep".

Additional question:

• Should there an option on prep material to force prepping this skipped no prep?

[StandingPadAnimations]

I don't think an option for force prep is needed. Assuming it's a user override, that should be respected always

[zNightlord]

I don't think an option for force prep is needed. Assuming it's a user override, that should be respected always

I'm just thinking about the case where you decide need prep material but have to go though each of them set it to 0 so.

[StandingPadAnimations]

Eh, I'd imagine the user would know what materials they've set MCPREP_NO_PREP on. Maybe that could be better solved with some UI design to remind the user which materials have no-prep? That might cause some cluttering though, so I'll tag @TheDuckCow on that

[StandingPadAnimations]

Overall I think we could put this under #274 (which I've been meaning to discuss more on for MCprep 4.0) and take a look at it later once we know how everything in a revamped system would fall in place

[TheDuckCow]

Very minor change requested, but once I see it I'd be happy to approve this as is. I don't see a reason to wait for something like this, and I actually like it better than the json approach we've been using so far (centrally defining rig names for checkups is kind of gross). I don't think this will interfere with the new material system planned, they can both coexist in my mind.

[TheDuckCow]

Looks good to me now, thanks for the change!