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. 
I've written that code before I knew about the design decisions behind services, would you mind removing that service cache and make them all disposable @aerych ?