Add a severity and acknowledgement filter for annotations

Add a severity filter, much like it is present in various
places in Zabbix, as well as a filter for the acknowledgement
status. This brings the interface closer to what is asked for
in https://support.zabbix.com/browse/ZBXNEXT-410

zabbix/partials/annotations.editor.html

@@ -21,6 +21,11 @@
     </label>
     <input type="text" style="width: 25em" ng-model='currentAnnotation.trigger' placeholder="Trigger name"></input>
   </div>
+  <div class="editor-option">
+    <label class="small">Minimum severity
+    </label>
+    <select class="small" style="width: 113px" ng-init='currentAnnotation.minseverity = currentAnnotation.minseverity || 0' ng-model='currentAnnotation.minseverity' ng-options="v as k for (k, v) in {'Not classified': 0, 'Information': 1, 'Warning': 2, 'Average': 3, 'High': 4, 'Disaster': 5}" ng-change="render()"></select>
+  </div>
 </div>
 
 <div class="editor-row">
@@ -38,5 +43,11 @@
     <label for="currentAnnotation.showHostname" class="cr1">Show hostname
       <tip>Show the hostname the event belongs to</tip>
     </label>
+    <input type="checkbox" class="cr1" id="currentAnnotation.showAcknowledged"
+           ng-model="currentAnnotation.showAcknowledged"
+           ng-checked="currentAnnotation.showAcknowledged">
+    <label for="currentAnnotation.showAcknowledged" class="cr1">Hide acknowledged events
+      <tip>Hide events, that have been acknowledged</tip>
+    </label>
   </div>
 </div>