Use GitMate in gitlab-ce and gitlab-ee projects

• Folks at GitMate have proposed we use their product directly in gitlab-ce and gitlab-ee.
• The product can be integrated with GitLab.com, and can do a number of smart automations.
• One of them is auto handling stale issues by labeling them. I.e. auto apply a label any issue that has had no updates after configurable x number of days.
• There are other features: https://gitmate.io/home