Validate format of project_url and token for GitLab CI service.

If `project_url` and `token` for are invalid, [service_hook creation](https://gitlab.com/gitlab-org/gitlab-ce/blob/7-13-stable/app/models/project_services/gitlab_ci_service.rb#L30-34) will silently fail due to validation of URL in `WebHook`.

Given that token is a sequence of numbers and letters for GitLab CI making sure that there are no unexpected characters should be enough to prevent service_hook being nil. 

Fixes #1997 

See merge request !987