fix(comments): add an activity when there is a new comment

so we will save as part of activity who should get notified about it.
and push an activity notification for those users so they can update
their activity list.

SD-684 SD-656

@ioanpocol what do you think?
yep 1 notification would be used in comments list widget to update that list, while the other would be used by this notifications list to let user know there is a new notification