Showing the wifi data usage results in reaching the max number of
threads in the pool executor. Switching the loader implementation
from Async task to AsynLoader and use a single loader to get the
whole list of preferences instead of using a new task to create each
list element.
Change-Id: I0da19ca09031a7fa178970c192e12a99ab489145
Fix: 33820327
Test: make RunSettingsRoboTests
