oriented USANS measurements

[pkienzle]

USANS on oriented models requires resolution integration over an oriented 2D pattern rather than a circularly averaged 1D pattern.

Sasmodels already includes the resolution calculator to support this.

Refactor sasview so that data+model come together in an experiment object that can compute the resolution smeared theory function. Use this object when communicating with the fitter and with sasmodels. This will place the resolution handling code in one place, where it will be easier to flag the data as oriented USANS, and trigger the appropriate resolution function.