Rework sample, atomic-weights, subclassing Sample, output functionality in Sample

• Rename sample data, coh and incoh is always used for coherent (collective) and inocherent (self) part of scattering functions
• Add total Fqt etc to sample
• subclass sample for dynamic and static
• add useful sample properties
• rework atomic-weighting with q-dependent form factors from Weights class
• Reshape static structure factor S(q) to (Nq, 1) to make it work nicely with all post-processing functions
• Fix bugs where static structure factor could not be spherical averaged
• some more tests

See these notes on interface design

Closes #120 (closed)