Add Calendar integration (read-only)

assets/calendar/widget.html

@@ -0,0 +1,16 @@
+<span class="dropdown maint">
+    <button type="button" class="btn maint-toggle{{if not .Count}} is-idle{{end}}" data-action="maint-menu" aria-haspopup="true" aria-expanded="false" title="Maintenance (H)">{{icon "maintenance"}}<span class="maint-count">{{.Count}}</span></button>
+    <div class="dropdown-menu align-right maint-menu">
+        <div class="panel-header">Today</div>
+        <div class="maint-list">
+            {{range .Today}}<span class="maint-when">{{.When}}</span><span>{{.Summary}}</span>
+            {{else}}<span class="muted">Nothing due</span>{{end}}
+        </div>
+        <div class="panel-header">Next 7 days</div>
+        <div class="maint-list">
+            {{range .Upcoming}}<span class="maint-when">{{.When}}</span><span>{{.Summary}}</span>
+            {{else}}<span class="muted">Nothing planned</span>{{end}}
+        </div>
+        {{if .PageURL}}<a class="btn btn-block maint-all" href="{{.PageURL}}">All maintenance →</a>{{end}}
+    </div>
+</span>