Readded Newton Cotes and Barycentric labs.

Also fixed spacing and figures in Newton Cotes lab.

Notes: the Newton Cotes lab needs revision. We could maybe get by with letting them work it as it is, but it warrants a more thorough reading.

Also, why don't we use b-splines for this sort of thing? I'm no expert, but intuition tells me that that would probably give really good results.