Refactored and improved view asserts
Refactored and improved view asserts

- Part of a reworking of the GMN internals that moves input validation
to a separate layer between the views and the database operations.
- Extensively reworked to support SIDs and obsolescence chains.

DataONEorg/d1_python,DataONEorg/d1_python,DataONEorg/d1_python,DataONEorg/d1_python