Refactored the descriptions of a number of structure user functions.
This includes the structure.align, structure.displacement, structure.find_pivot, structure.rmsd and
structure.superimpose user functions. The paragraph_multi_struct and paragraph_atom_id module
strings have been created and are shared as two paragraphs for each of these user function
descriptions. This standardises the pipe/model/molecule/atom_id descriptions. The user function
wizard page sizes have been updated for these changes.
