Fix duplicate shifts on mobile views

If the calendar loaded the listWeek view by default, which it does on mobile, it was then switching the date for the calendar immediately after -- this was causing events to appear in the list twice. We now initialize the right start date for the listWeek view to stop this from happening.

uber/templates/staffing/shifts.html

@@ -598,7 +598,7 @@ <h2 class="accordion-header" id="restricted-jobs-info-header">
 
   const ec = new EventCalendar(document.getElementById('shift_cal'), {
         view: window.matchMedia('(max-width: 576px)').matches ? 'listWeek' : 'timeGridWeek',
-        date: '{{ c.EPOCH.date() }}',
+        date: window.matchMedia('(max-width: 576px)').matches ? '{{ start }}' : '{{ c.EPOCH.date() }}',
         allDaySlot: false,
         highlightedDates: {{ highlighted_dates|safe }},
         headerToolbar: {