Check for null AND undefined in mention filter

Also, add dark style of @all and @me mentions.

src/filters.ts

@@ -152,7 +152,7 @@ angular.module('3ema.filters', [])
                             cssClass = 'me';
                         } else {
                             const contact = webClientService.contacts.get(possibleMention.substr(2, 8));
-                            if (contact !== null) {
+                            if (contact !== null && contact !== undefined) {
                                 // Add identity to class for a simpler parsing
                                 cssClass = 'id ' + identity;
                                 mentionName = contact.displayName;

src/sass/components/_mention.scss

@@ -5,17 +5,17 @@
     border-radius:5px;
     line-height: 10pt !important;
 
-    &.me {
+    &.me,&.all {
         background-color: #8b8b8b;
         color: white;
     }
 
-    &.id,&.all {
-
+    &.id {
         box-shadow: 0 1px 1px rgba(0,0,0,0.1);
         color: black;
         background-color: #E0E0E0;
     }
+
     &:before {
         content: '@';
         font-size: 10pt;