CrystalOrientation rename to SampleFrame (#245)

[stestoll]

This changes the way a sample orientation is defined in the lab frame (see issue #245). This makes the frame interface more consistent (lab -> sample -> mol -> tensor instead of lab <- sample -> mol -> tensor).

Main tasks:

• [x] rename all instances of Exp.CrystalOrientation to Exp.SampleFrame
• [x] invert definition (Exp.CrystalOrientation defines crystal -> lab frame transformation, Exp.SampleFrame defines lab -> crystal frame transformation)

List of additional necessary updates , changes and checks:

Functions:

• [x] add tests for Exp.MolFrame and Exp.SampleFrame
• [x] add tests for Exp.SampleRotation
• [x] add tests for space group site rotations (based on Exp.CrystalSymmetry)
• [x] consistently detect powder vs crystal vs partial order sims from Exp.MolFrame, Exp.CrystalSymmetry and Exp.Ordering in all sim functions
• [x] treat obsolete fields Exp.Orientations and Exp.CrystalOrientation consistently across all sim functions
• [x] check all functions that rely on phi and theta (mol -> lab frame): either adapt interface or clarify documentation
• [x] in particular, check levelsplot - currently needs phi/theta input

Partial ordering:

• [x] change Exp.Ordering angle definition to conform with Exp.MolFrame
• [x] check chili protein director frame definition (plus documentation)

Documentation:

• [x] update release notes
• [x] update sim function documentation
• [x] check all documentation for consistent use of "sample frame" vs "crystal frame"; mention that this also applies to films etc.
• [x] update crystal sim user guide

Examples:

• [x] update crystal rotation example
• [x] check all crystal sim examples (incl. triplet_crystal_spinpolarization)

Downstream:

• [x] consider eliminating Exp.SampleRotation - decision: keeping it
• [x] consider eliminating rotplane - decision: removing it
• [x] consider absorbing Exp.Ordering into Exp.MolFrame - decision: keeping it, not to overload MolFrame

[stestoll]

Thanks! I fixed the docs. The test resfields_frames passes on my computer, with an error of 5e-14. I'll fix the lab frame definition for the superconducting magnet after the merge. An additional example for Exp.Ordering is a good idea, I'll add that after the merge.