Fix various bugs when tracking deployments
This fixes the following issues in the deployment tracking code:
- "environments" was used instead of "env" in release.rake.
- GET parameters were not supplied correctly in ReleaseTools::GitlabClient.deployments.
- Adding a comment that consists out of just a slash command is rejected by the API. To work around this we now use the merge request edit API to add the workflow labels.
- The commit range for QA issues was returned in the wrong order: latest..previous instead of previous..latest
- In release.rake we used the wrong constant for notifying merge requests of deployments to the pre environment.