This app can detect whether other users of the app are physically in your neighborhood. In general terms, the minimal required functionalities are:
* You are able to create an account, log in and log out.
* Show your own location with a marker on a map.
* Show also the location of the other logged in users of this app with markers on the map, including their names (use different colors: one for your own marker and another one for the other users). When a user is not logged in, he should not be visible.
* Give a message and vibration signal when one of these users comes nearby of your location
