comments: allow commenting on empty files without content.

comments: ensure we ALWAYS display unmatched comments.

diffs: make validation of version, so we can change diffs and force re-cache if diffs are in old version.

git: use a fetch_sync based creation of remote repos. - skips fragile dulwich code that has problems with large repos - is in sync with logic that does remote fetch - is faster and more efficient

mail: use faster detection of email misconfiguration. This should be done at earliest possible step to prevent from DB query for recipients if we wont send email anyway.

core: handle edge case requesting matched routes but with hg/svn/git or api context. - before we error out with 500

docs: updated example hooks line

import/repo-checks: skip validating storage path in detection of SCMs.

license: update license metadata and generation code

validators: fix url_validator tests and make it flag controllable.