utils: adopt now() (renamed to timestamp()) and parse_timestamp(), test them

utils: a small module for shared functions, the first of them is rel()

checker: remove duplicate "job failed" message Now that every failed run() is covered in the execute() by return False, one such message in wrapper() is enough.

checker: print requested linters without duplicates Also, some linters could come preinstalled (compiled, as distro packages), so they don't necessarily need to be installed.

viewer: request light fields when using just metadata from Check / and project pages just link to checks, so the heavier text fields like Check.lines aren't actually important, and can be excluded from SELECT for a nice performance boost.

tests: test parsing urls with "directories"

incoming: support --help and --debug, and read from stdin by default

checker: actually, let's just redirect docker-build stdout to stderr instead

checker: pass arguments reliably straight to python -u

checker: ignore docker-build stdout