incoming: only try to match linter output if it's not a meta line

incoming: skip checking the whole line when it's linter output When a line starts with a certain pattern, it's recognized as linter output, but determining if it's an error or a warning was done looking at the whole string again multiple times. Let's save on regexes and look only on the important part.

viewer: inherit from BaseHandler for catch-all 404 pages too

viewer: templates for 404 and 500 error pages

tests: create the in-memory database once in setup_module() Also mock the correct method, close() instead of disconnect().

viewer: get_or_404() to raise 404 (instead of 500) when model doesn't exist

tests: test index page and a non-existent page that gives 404

tests: mock database to be an in-memory db for tests

tests: add test_models with some Check.get_duration() checks

viewer: don't show "0 sec" in get_duration() if check took exactly X minute(s)