add calendar loader

assets/js/components/Calendar.vue

@@ -48,6 +48,9 @@
 
         <div class="row" v-if="weeks.length > 0">
             <div class="col-md-12">
+                <div v-if="loading" class="text-center">
+                    <div class="spinner-border text-primary" role="status"><span class="sr-only">Loading...</span></div>
+                </div>
                 <table class="table table-bordered mt-3" v-if="!loading">
                     <Week v-for="week, key in weeks" :key="key" v-bind:week="week" />
                 </table>