Use GeoLocation Class & Store Last Location

To address issues with the fact the location manager will purge the
last known location pretty quickly this commit will retain the last
location that was locked through GPS, this is then used for any methods
that require a location such as some OpenCellID functions when there
is no GPS lock and the users location can not be determined through
cached information.
Exit Button Fix

This commit makes the drawer menu exit button actually exit the activity
instead of doing absolutely nothing at all!
MapViewer Cell Info Display Fix

Add MCC & MNC details to the Map Marker display window for local database
cell information, this was already displayed for OpenCellID Cell info
but was not added to the tracked cell details loaded from the local
database.
Extra Google Play Services Check

Added an additional check for Google Play Services prior to starting the
MapViewer to attempt to address NPE issues users were still facing with
loading the MapViewer WITHOUT Google Play Services installed.
Automatic Cell Monitoring Preference

Added preference for Automatic Cell Monitoring which is now ENABLED by
default, user can choose to disable automatic monitoring through the
preferences fragment.
Database Viewer: Fix Silent SMS NPE

Correct NPE experienced when trying to view the Silent SMS database
contents.
Minor Code Cleanup
Merge pull request #120 from xLaMbChOpSx/master

Grabbing the latest code
Update CHANGELOG.md