Thumbnails in submission forms rendered incorrectly

[ybnd]

Describe the bug
In submission, Relationships in the form don't load thumbnails and don't scale placeholder font correctly.
We've seen the same issue in other places before.

To Reproduce
Steps to reproduce the behavior:

1. Start a submission in a Collection that has a Relationship field in one of its forms
2. Add a Relationship by lookup
   (Refresh the page so that the new Relationship show up, see Adding relationships through submission doesn't update view automatically #1671)
   • Thumbnail placeholders will appear even for Items that have thumbnails (missing followLink?)
   • Thumbnail placeholder text does not resize for narrow viewports

Expected behavior
Thumbnails should appear and placeholder text should scale in the same way as it does in search/browse/edit/...

Related work
#1780
#1883

[tdonohue]

Pulling this over to 7.5 board & flagging as high priority. I suspect this is just a minor CSS related issue. @mspalti : pinging you in case you have time for a quick fix. Volunteers welcome.

[mspalti]

@tdonohue, I'll take a look.