Show branch names when starting a pipeline from the middle

[wahapo]

What happened: When user is using branch filtering and start a detached job, user is confused as to whether the job will run on the pipeline branch or on the branch from which it was triggered. Many users mistakenly believe that it is executed in a pipeline branch.

What you expected to happen: It would be nice to see the branch name when user clicks Start pipeline from here.

How to reproduce it:

1. Select event with started from branch filtering. (ex. https://cd.screwdriver.cd/pipelines/6422/events/605399)
2. Click Start pipeline from here for the detached job.
   
3. Click Yes.
   
4. Some users misunderstand that a build is started using a pipeline branch.