Bug 832335 - [Clock] Display Alarm set notification inside Analog clock face

Refactors banner notification code to:

* move banner animation to above the bottom of the screen, giving the user a hint that the element can be dismissed and doesn't displace more persistent alarm indications.
* add unit tests for the creation and format of the banner notification
* move the call to `banner.js` out of `AlarmManager` and into the save callback of `AlarmEdit` to separate concerns between rendering and database interactions.