Newcubesummary testsaffected

[pp-mo]

Just a draft, opened to run the tests, replacing stephenworsley#8

Not ready for merging yet

• includes all content from Refactor cube summary #3952
• unit-testing is totally crude at present, needs breaking apart to test individual aspects.
  (I have a list somewhere)

This gives a headsup on ideas for the new code : CubePrinter converts CubeSummary into string reprs

This PR also plugs that mechanism into the cube string repr methods : cube.summary, .__str__ and .__repr__
This should show the effect on the tests

CURRENT STATUS:

• problems with repr-html (working on it)
• beautiful table to be added to the dependencies...

[pp-mo]

Bit nasty using pip again, but to fix we would need to create a recipe + builds (conda-forge)

The tests are now giving some idea of what it takes to integrate these changes (or similar)
But I am also working on that : some bugs uncovered + changes already in planning

[pp-mo]

Problems are already as few as 13 test failures.
I am still experimenting with slackening off the precision of some of these (ignoring some whitespace).
Also, some of the remaining presentation changes may be acceptable/desirable

[pp-mo]

Closing in favour of #3982 (or its successors)