Twitter API: user's name is expected to be set.

I keep finding users who don't have display name set, and this results in notifications such as "null favorited a status", and notifications and ugly spaces in pleroma-fe like this:

(ignore that posts are called 'mews' on my instance...)

We could be returning the user's address/login name as their name in Twitter API queries if they don't have one, or it could be fixed in the frontend.