Show commit status from CI on commit lists and details view

The status is stored as git notes, using the 'ci' namespace. Although I'm using Jenkins as CI and the publish functionality from git plugin, there is nothing specific to Jenkins, although the CI user needs write permission to push notes into the repository. Fixing #316 (closed) is not strictly required, but it should reduce the noise (I did submit !185 (closed) for that purpose).

This is well tested in our 7.2 & 7.3 deployment, but as I've seen that at least current omnibus packages use rugged to interface the repositories, I've included support for it. This support is not so well tested, and it is not straightforward, as rugged current implementation only supports default namespace for git notes. If you point me to the right location, I will add a bit of documentation about this, including the expected format for ci git notes

Currently I'm also extending this approach to get a CI service alike integration for Jenkins, to show status badge on project view and merge requests. Other future work is extension of current API to not require write permission.