From hierarchical view, one of root cause is PreferenceCategory.
Looks like PreferenceCategory generates an invisible space when
we add a footerPreference as a child.
So, we remove PreferenceCategory directly, and declard "allow divider"
attribute for neccessary preferences.
Test: Visual
Fixes: 130396913
Change-Id: I6d56ac165633aa211e794e07417821066380d041