Improve markup detection, fixes #4695

Add support for reStructured Text markup language

Bump version of gitlab-shell to 1.7.0

Fixed Fixed issue when project default branch selected from non-exists and UI does not allow to change it

Fix notifications to handle participants and mentions on commits too

Add 'repository' to path blacklist, fixes #4591

Better description based on a conversation in the contributor room.

Reenable the create project button after errors

Currently if you try to create a project from an existing repo but give it a bad
URL, you see the "Import url should be a valid url" error and the form, but the
submit button is disabled meaning you can't fix the URL and resubmit the form.
This fix just enables the button when the project has an error.

Closes #4070