Refs #10283. Modified PointGroupFactory to accept space group symbols
Refs #10283. Adding a symbol to ReflectionCondition
Refs #10283. Adapted CrystalStructure.
Refs #10283. Added more documentation.
Refs #10283. Added unit test for comparison

Using ReflectionCondition and structure factor calculation should give the same result for the same input.
Refs #10283. Moving calculation of F and d

Putting those calculations in their own methods makes it easier to add other calculations later.
Refs #10283. Re-adding F^2 method to BraggScatterer
Refs #10283. Adapting CrystalStructure to final design of scatterer
Refs #10283. Suppressing some gmock warnings.
Refs #10283. Adding possibility to clear CompositeBraggScatterer.
Refs #10283. Some cleaning up in CrystalStructure
Merge branch 'feature/10283_adapt_crystal_structure' into develop