Watch the settings DB narrowly for alarm stream volume changes

Bug: 28139617
Bug: 28146131

The settings DB is now observed more narrowly on the URI:
content://settings/system/alarm_volume_speaker and thus only
displays the warning snackbar in response to true volume
adjustments and not other incidental settings db changes.

Change-Id: Idfb134a6eeaea074ece39264f2b50f4ddb1c3303