Comment hot fix

Closes #2929 
Refs #2894 
Adds back the ability to reply to and edit comments on a self-hosted site. 
Adds new functionality for displaying an avatar image when `avatarImageForDisplay` is nil 
Fixes an issue with how the return value of the call to wp.editComment was used. 
My understanding is that service instances should be disposable and not cached, hence the code is written that way. Maybe I'm misinformed?