ChangeScreen2: Remove reviewers using [X] in "chip"

If the current user can remove a reviewer, add a "[X]" button to the
right of the reviewer's name in their chip in Reviewers or CC. After
removing an entry the screen is reloaded to rebuild the correct data
for Reviewers, CC and the labels.

Bug: issue 2067
Change-Id: I9c69f46036dd2eeb39eb3d85c9e9d0d6fe6f64f1
7 files changed