[IMP] mail: channel seen icon indication ('v' and 'vv')

This commit adds the seen icon next to a message for all channels
except livechat.

It tracks received and seen messages for all members of the channel.
Icon is either 1 or 2 check(s) ('v' or 'vv').

Those are the different states of this 'seen' icon:

  ICON:                           DESCRIPTION:

  no check .................. no one has received the message.
  1 check ................... some members have received the
                              message, no one has seen it.
  2 checks (greyed-out) ..... some members have seen the message,
                              some or everyone has received it
  2 checks (green) .......... all members have seen the message

This icon is not shown for messages preceding the last message seen
by everyone, in order to reduce visual noise.

Task-ID 1881001

1 files changed, 10 insertions, 0 deletions

diff --git a/addons/mail/static/src/js/models/threads/abstract_thread.js b/addons/mail/static/src/js/models/threads/abstract_thread.js
index 829f54581da..d6a37967c68 100644
--- a/addons/mail/static/src/js/models/threads/abstract_thread.js
+++ b/addons/mail/static/src/js/models/threads/abstract_thread.js
@@ -103,6 +103,16 @@ var AbstractThread = Class.extend(Mixins.EventDispatcherMixin, {
         return !_.isEmpty(this.getMessages());
     },
     /**
+     * States whether this thread is compatible with the 'seen' feature.
+     * By default, threads do not have thsi feature active.
+     * @see {mail.model.ThreadSeenMixin} to enable this feature on a thread.
+     *
+     * @returns {boolean}
+     */
+    hasSeenFeature: function () {
+        return false;
+    },
+    /**
      * States whether this thread is compatible with the 'is typing...' feature.
      * By default, threads do not have this feature active.
      * @see {mail.model.ThreadTypingMixin} to enable this feature on a thread.