DeskClock: add runtime permission control and ringtone fallback process

(1) when one alarm alert ringtone has been deleted, and its ringtone
should be fallback to default ringtone

(2) when ringtone need storage runtime permission, but the permission
is denied, and should fallback too

(3) optimize the ringtone title display for such as audio ringtone type

(4) during setting ringtone and if user denied permission, fail current
settting and give user toast prompt

Change-Id: I310ad9c81657f6b1a09a1bc53098e9c204bb3bae
CRs-Fixed: 1021348