Revert "Revert "Convert BT preference to use TwoTargetPreference""

This reverts commit 457c3cbe.

Revert with fix/test.
The fix is that we removed DevicePickerFragment#initDevicePreference(),
which incorrectly set a useless widget on preference, and removes the
gear icon from preference, preventing bind() call to go through

Change-Id: Ia70cdb51d13cca6035a4e7fe8008d195f7f00c6e
Fix: 36511169
Test: runtest --path tests/app/src/com/android/settings/bluetooth/DevicePickerActivityTest.java