Additional enhancements to Jira integration

Dev: https://dev.gitlab.org/gitlab/gitlabhq/issues/2162

To strengthen our competitive position against Stash, additional enhancements to the Jira integration maybe needed.

Some areas include:

• See related commits(gitlab-ce#5854) and branches and merge requests in a JIRA issue-DONE.
• Create GIT branches from within JIRA.
• See the some details of JIRA issues in GitLab
• See the JIRA issues related to GitLab commit and pull requests

Marin

1. Can be done
2. This is in Jira and unless it has some sort of custom command or custom trigger to execute a call to our API we cannot do anything about it
3. Same as previous
4. Do not understand this one

Regarding no. 1, reference is already created (since 7.8) for any commit, issue or MR with mention like JIRA-123 in comment. I don't really understand how they expect branch to be referenced but I suspect that something like 123-branch-name that would put a reference in an issue is doable and can be done with some effort.

Related to

• https://gitlab.com/gitlab-org/gitlab-ce/issues/5541
• https://gitlab.com/gitlab-org/gitlab-ce/issues/5994

cc/ @Haydn @marin @sytses @dzaporozhets