Node mentions do not have placeholder image

Added new image and extended MentionsType plugin for node.

Might want to instead consider 🐛 Avatar should be optional Active which just removes the requirement for avatar.

How about fetching image data from default field like user_picture ? (ex: field_image)

> How about fetching image data from default field like user_picture ? (ex: field_image)

There's no default image field in node. It might be anything and different for each node type. From my point of view, #3512131 is the only appropriate way. If someone wants to display images for nodes, there are plenty of ways to add an image token to the response.

@jaydarnell could you test if 3512131 resolves you issue?

I think MR !25 #3 solves the problem. I use it without any problems.
It may be a suitable solution for those who want to add placeholder images for node type mentions instead of the solution suggested in #3512131.
+1 for RTBC