Open ends for crystallization/PBM

[jbreue16]

There are some smaller open ends for the crystallization code that should be addressed soon.

• Review documentation @WFlynnZ
  • wording of the three parts: fragmentation, aggregation, formation ?
• Finalize CADET-Verification EOC tests: Add EOC tests for aggregation and fragmentation in crystallization CADET-Verification#44 @WFlynnZ and @jbreue16
• Add a test with mode 7 (all terms combined) to cadet-core. This should include both the numerical reference and Jacobian test just as we did for the other modes @jbreue16 , done in [Add test for crystallization with combined PBM, agg. and frag. in a CSTR #401]

Another open end regarding performance is tracked in a separate issue since a timely fix is not planned.
#392