Added a screen to configure wireless scanning

- Created "Scanning" preference screen

- Added overflow menu on "Location" settings to access "Scanning" settings

- Moved "Wi-Fi scanning always available" from Wi-Fi settings to "Scanning"
  settings

- Added "Bluetooth scanning always available" preference (UI only)

Change-Id: I85d8cd60ab309db5db9caee43f4b5a117192d904