Merge branch 'pivotaltracker-restrict-branch' into 'master'

Ability to restrict branches for pivotal tracker integration

## What does this MR do?
It allows to specify branches which you want to track for pivotal tracker integration.

## Why was this MR needed?
Typical use case: send commits to PivotalTracker and finish the story only when the feature branch is merged into master.

See merge request !5752