Numerous minor updates for Bluetooth Settings

+ Remove top "this device" item from the list
+ Upon opening Bluetooth settings, cue a search for available, pair-ready devices
+ Upon opening Bluetooth settings, make the phone/tablet visible to other devices
+ Keep phone/tablet visible as long Bluetooth settings is open and screen is on
+ Filter this list so that only pair-ready devices are displayed
+ Add non-interactive text “<Device name> is now visible to nearby devices” at the bottom of the available devices list

Overflow menu:
- Remove “visibility timeout”
+ Replace “Search for devices” with “Refresh”

Bug: 15716927

Change-Id: I7c5225784af9bfb48dde511e05503ddc59be2b2b