PBN static analysis

[daemontus]

Currently, we can parse a network and check if it is correct, but we can't really handle anything more. We should be able to detect at least some basic stuff:

• find outputs (and remove them)
• find inputs (and convert them to parameters)
• check if we satisfy the monotonicity constraints (this can be done by constructing the async graph, but that is tedious and error prone, a better method is needed)
• check for unused parameters and variables
• check for missing/invalid metadata and similar stuff
• some more advanced stuff - flattening chains, inferring monotonicity from function, some structural analysis (SCCs of the regulatory graph, positive/negative feedback loops, etc.), look at cell collective.

This is potentially related to #4, because we might need some "warning highlighting", but that is a minor thing. However, we should have some universal mechanism for reporting errors and warnings and relating them to parts of the submitted string format (maybe have a look at language servers?).