Add title tag to work indicator

public/i18n/de.json

@@ -148,7 +148,8 @@
         "MESSAGE_TOO_LONG_SPLIT_SUBJECT": "Nachricht aufteilen.",
         "MESSAGE_TOO_LONG_SPLIT_BODY": "Es werden maximal {max} Zeichen pro Nachricht unterstützt, wollen Sie die Nachricht in {count} separate Nachrichten aufteilen?",
         "BALLOT_MESSAGES_NOT_SUPPORTED": "Umfragen werden in Threema Web derzeit nicht untersützt.",
-        "NICKNAME": "Nickname"
+        "NICKNAME": "Nickname",
+        "THREEMA_WORK_CONTACT": "Threema Work Nutzer"
     },
     "messageTypes": {
         "AUDIO_MESSAGE": "Sprachnachricht",

public/i18n/en.json

@@ -149,7 +149,8 @@
         "MESSAGE_TOO_LONG_SPLIT_SUBJECT": "Split Message",
         "MESSAGE_TOO_LONG_SPLIT_BODY": "No more than {max} characters can be sent per message, do you want to split it into {count} separate messages?",
         "BALLOT_MESSAGES_NOT_SUPPORTED": "Ballot messages are not yet supported in Threema Web.",
-        "NICKNAME": "Nickname"
+        "NICKNAME": "Nickname",
+        "THREEMA_WORK_CONTACT": "Threema Work user"
     },
     "messageTypes": {
         "AUDIO_MESSAGE": "Audio Message",

src/directives/avatar.ts

@@ -108,7 +108,9 @@ export default [
                     <div class="avatar-loading" ng-if="ctrl.isLoading">
                         <span></span>
                     </div>
-                    <div class="work-indicator" ng-if="ctrl.showWorkIndicator()">
+                    <div class="work-indicator" ng-if="ctrl.showWorkIndicator()"
+                        translate-attr="{'aria-label': 'messenger.THREEMA_WORK_CONTACT',
+                            'title': 'messenger.THREEMA_WORK_CONTACT'}">
                         <img src="img/ic_work_round.svg" alt="Threema Work user">
                     </div>
                     <img