Added support to trigger job only if assigned to specific user.


![image](https://cloud.githubusercontent.com/assets/3033505/5262387/951f1b5a-7a25-11e4-9515-011f560c4da7.png)

Added support to trigger job only if assigned to specific user.
Added trigger comment to force job to run without new commit to Merge request.

Since i'm new to github and not a programmer I would appreciate some help reviewing this feature.
We have been running it for a few weeks now with good results.

Our worklflow looks like this:
When a MR is created or committed to JOB1 triggers and build a docker-image for later use.
When the feature is tested and reviewed its assigned to Jenkins user and JOB2 is triggered that runs unit-tests, linter-tests, starts the previously created docker-image and runs gui-tests. If successful the feature is merged and pushed.