Mass ordering check omega check

This MR builds upon !8 (merged) (i.e. it's a branch of it) and adds another test to check that Omega from Omega-vs-time is monotonic.

@edward.fauchon-jones I've added it as a format2Interfield check which isn't strictly true... But I think it's fine. Not perfect. Do you think we should add another test field? format2GeneralTests ?

My build is breaking too. I can't figure out why. When you get a chance it would be great if you could take a look.

THANKS!!!