Forward-port: add increasing volume option for alarm clocks

this commit adds a checkbox preference for "increasing volume" to
alarm clocks. when checked, the alarm will start off at 10% of the
system-wide alarm volume and slowly increase to 100% over the
course of a minute.

Changeset 2: rebase sloppy mess after somebody managed to "splice out" one of my intermediate commits... *facepalm*

Change-Id: Icf3d3eb3e033d70ebc30e8aad7f9cdf8f5438f3a