$('#tracker_button').on('click', function() { start_tracking($('#tracker_username').val()) });
$('#tracker_stop').on('click', stop_tracking);
$('#tracker_button').on('click', function() { start_tracking($('#tracker_username').val()) });
$('#tracker_stop').on('click', stop_tracking);
$('#track_user').on('click', function() { stop_tracking(); start_tracking($(this).data('user')) });
if(localStorage.getItem('tracker_username'))
$('#track_user').on('click', function() { stop_tracking(); start_tracking($(this).data('user')) });
if(localStorage.getItem('tracker_username'))