The new endpoints wrap the existing star endpoint, making it easier for
users to mute changes by a simple PUT, without input, rather than
having to construct a POST request with the necessary stars input.
The endpoints also provide "Mute" and "Unmute" buttons on the UI.
The buttons are not displayed for own changes.
Change-Id: Iab3de63e47bf7a850d8718febff326bc550c3abd
e8647c699f