Reduce jank in wifi settings

 - Fix view recycling for AccessPointPreferences by adding a dummy
   during initial inflation
 - Cut down on what is done during onBindView and refresh()
 - Try to re-use AccessPointPreferences when possible

Some jank still occurs when scan results come in, but it is less
than before.

Bug: 16518752
Change-Id: I2619303281dd50aa3864783c49738ae9f221834a