List generic commit statuses individually in MergeRequests#show

Created by: dsander

The GitLab 8.1 added the commit status API, this is my attempt to expose the external commit statuses to the user.

This changes the status indicator of a MergeRequest, before all CommitStatuses were grouped into one status which did not show information about the status of external (GenericCommitStatuses) statuses. Now CI::Build statuses are still grouped together, but GenericCommitStatuses are shown individually including the description and link to the status/build information.

Before, one could not see which commit status failed and which succeeded:

After, external commit statuses are shown individually: