Test suite: run all notebooks in one or more dirs rather than explicitly named notebooks

[willfurnass]

Currently explictly list the notebooks to be run in tox.ini. A cleaner approach would be to have

• one or more directories within which all notebooks should be run
• one or more distinct directories in which notebooks aren't automatically run

[willfurnass]

@jarmarshall @joefresna Which notebooks should/shouldn't be run by tox?

[jarmarshall]

I would say run everything (including in subfolders) in:

• docs
• TestNotebooks
• DemoNotebooks

[willfurnass]

Getting this sorted has proved more difficult than first anticipated - our CI jobs already take ~50 mins to run (Issue #366) and attempts to run additional notebooks so as to address this issue keep resulting in cell execution timeouts (see PR #363). Bump this Issue to 1.2.0?

[jarmarshall]

I'm happy with that - stick it on the second release milestone for now I think...

[willfurnass]

@jarmarshall How about we migrate all Notebooks other than the user manual and test notebooks to other repos to cut down CI job time? These auxillary repos could have their own CI and could depend on stable versions of MuMoT.