flake8 changes and tidies
Move fixups into tiddlyweb.fixups to be more DRY

Otherwise there's a lot of duplication in the various modules.

By centralizing these I'm not try to assert that they solve
things correctly, rather put them in one place.

Note that some modules do their own customizations instead of
using the centralized fixups: They require special behavior.
Begin the process of flake8 the tests.

Which is for the sake of future...expansion?