Settings: fixed battery stats app list

http://jira.omnirom.org/browse/OMNI-493

The check of mAppListGroup getPreferenceCount is no longer working
after we added other options on this page. Add a separate counter to get
back the full possible list of 12 apps

PS3:
IMHO the number of apps should be 10 if we have
MAX_ITEMS_TO_LIST = 10

Change-Id: I679b01deec0f52d4fa2012a31b7b305f8fe176b5