Fix #903 Create StaticTransform, Frame.getStaticTransformTo, and supporting methods
StaticTransform is a new interface that only include information for transforming positions and directions. Transform is a subtype.
Added a getStaticTransform() method to Frame. Some testing of this MR has shown a speed up of 1.9 compared to using getTransform() when transforming positions. This is because StaticTransform.combine(...) can ignore all the velocity and acceleration terms. (And that Orekit is very good at caching frame transforms so the full precession model is rarely evaluated.)
Feedback welcome, especially with regard to the name staticShiftedBy(...)
which I'm not sure conveys its meaning well.
More can be done to not compute quantities that are not used. See #903 (closed) for a list.