viewer: add proper markup to changeset date so it's picked up by moment.js

viewer: restyle regular badges to be a bit more like status badges In practice, it means: no border, 3px rounded corners and more pronounced text shadow.

viewer: setup and clone tasks without errors/warnings are collapsed by default In addition to errors and warnings, which leave task expanded, target line also does the same, so sharing a link to a specific line doesn't surprise people by hiding the line somewhere.

incoming: remove linkstart and linkend until things are actually ready

tests: test read_linter_config() from checker.py

tests: test run() from checker.py

incoming: save linkstart and linkend for lines (not used yet)

viewer: make task blocks collapsible (except cleanup)

incoming: use a subquery for Check.ordinal instead of a separate query

models: drop Check.raw field (not worth storing in the same table) Replaying checks can be done (and is easier) when storing checker output in plain files, so let's lighten up the load on the database.