Add first day of the week feature to user settings and calendar functionality

backend/templates/calendar.html

@@ -26,7 +26,7 @@
     </div>
 
     <ul class="weekdays">
-        {% for day in [
+        {% let day_names = [
             Sentence::CalendarMondayAbbreviation,
             Sentence::CalendarTuesdayAbbreviation,
             Sentence::CalendarWednesdayAbbreviation,
@@ -34,9 +34,16 @@
             Sentence::CalendarFridayAbbreviation,
             Sentence::CalendarSaturdayAbbreviation,
             Sentence::CalendarSundayAbbreviation,
-        ] %}
-            <li class="weekday">{{ context.tr.t(*day) }}</li>
+        ]  %}
+
+        {% for i in 0..7 %}
+            <li class="weekday">
+                {{ context.tr.t(*day_names[
+                        (i + context.first_day_of_the_week().num_days_from_monday() as usize) % 7
+                    ]) }}
+            </li>
         {% endfor %}
+
     </ul>
 
     <ul class="days">