Alert Dialogs fix

When the user does not have networks connection or the GPS in not
enabled, the user is asked to enable them both in order to use the
application.

The bug was that when the orientation was changing the alerts were
appearing on every onResume() call.

I fixed with boolean flags. This way the alerts show only once and the
user gets Toast messaged when trying to get the venues that he does not
have network connection or GPS enabled.