Adding GitLab 8.8 info: upgrade instructions, links to apps, troubleshooting tips (!773) · Merge requests · GitLab.org / omnibus-gitlab · GitLab

Do not update/delete: Banner broadcast message test data

Do not update/delete: Notification broadcast message test data

username-removed-203201 requested to merge it33/omnibus-gitlab:patch-1 into master May 12, 2016

Adding special upgrade instructions needed for upgrading to Mattermost 3.0 using GitLab 8.8
Clarifying option for managing Mattermost settings in gitlab.rb
Adding links to new mobile and desktop app downloads
Added trouble-shooting tips/FAQs to end section