kwalitee: grep-like output and exit status changes

• Produces grep-like filename:linenumber output for kwalitee findings and returns exit status 0 if all checks passed, 1 otherwise.

• Standardises upon '[INFO]' and '[ERROR]' instead of '>>>' in output headings.

• Cherry-picked from 5b6f2403d1da035725da2753eccc8078281d79f2.