feat(mail): filter mailbox by unread messages

Fixes #1146
Fixes #3156
Fixes #4752

UI/WebServerResources/js/Mailer/Mailbox.service.js

@@ -342,6 +342,17 @@
     return angular.isDefined(this.$selectedMessage);
   };
 
+  /**
+   * @function toggleUnseenOnly
+   * @memberof Mailbox.prototype
+   * @desc Toggle filter by unseen messages only. Requires a round trip to the server.
+   */
+  Mailbox.prototype.toggleUnseenOnly = function() {
+    var _this = this;
+    this.$unseenOnly = !this.$unseenOnly;
+    this.$filter(Mailbox.$query);
+  };
+
   /**
    * @function $filter
    * @memberof Mailbox.prototype
@@ -394,6 +405,9 @@
       options.syncToken = this.$syncToken;
     }
 
+    if (this.$unseenOnly)
+      options.unseenOnly = 1;
+
     // Restart the refresh timer, if needed
     if (!Mailbox.$virtualMode) {
       var refreshViewCheck = Mailbox.$Preferences.defaults.SOGoRefreshViewCheck;