New api to sync zen mode state from listeners.

 - Allow connected listeners to request changes
   to the primary device's interruption level.
 - Rename alerts -> effects in the other constant,
   which does not affect interruption level.
 - Rename "flags" -> "hints"
 - Basic NoMan wiring for level hint.

Bug:15888672
Change-Id: I2b07fb2c9d32a143fff7c260b7d2cd4d0cd3a592