feat(datepicker): drop native datepickers in favor of AirDatePicker for better compatibility

As Firefox (still) doesn't support month input type

app/templates/monthly_overview/pages/overview.html

@@ -124,7 +124,8 @@
       <div class="collapse" id="collapse-filter">
         <div class="card card-body">
           <form _="on change or submit or search trigger updated on window end
-                   install init_tom_select"
+                   install init_tom_select
+                   install init_datepicker"
                 id="filter">
             {% crispy filter.form %}
           </form>