Add device name to About Phone page.

The device name is reflected in three places: A Settings.Global flag
which can be read by third party apps, the Bluetooth device name, and
the Wi-Fi tethering hotspot name.

The Bluetooth and Wi-Fi names can be changed independently of the device
name, but if the user sets the device name, they are all changed in
parallel.

Due to the naming restrictions of Bluetooth devices and SSIDs, the SSID
naming restrictions apply to the device name.

Bug: 63819909
Test: Robotest
Change-Id: I3a81535fc07d183557a6fa5d54baef3c7868499c