validation for process completeness

**Problem**
A process with linked protocols and output files but missing input biomaterials or files passed graph validation

**Solution**
I would like a test to check that each process is linked to at least:
- one input biomaterial or file
- one protocol
- one output biomaterial or file

From a spreadsheet it's easy to see if one of the three is missing, but from the ui it's not.
This test would be particularly helpful when we have to modify the linking through the ui and it's harder to check if we missed something.