Cahvor Distortion (#503)

* Adds CahvorDistortion mixin for MSL

* Small CahvorDistortion fix and adds test for CahvorDistortion

* Fixed CahvorDistortion to return all zero coefficients and offsets if no OR(E) in model

* Changed cahvor distortion test

* Reduced number of lines in line scan cameras if we don't care about the exact ck times

* More cahvor stuff

* Addressed PR feedback

* Removed extra line reduction code

* Updated math to compute x, y distortion offsets

* Changed assert to assert_allclose