fix(identities): Split out "username" profile and protect it

[castaway]

Fixes #1463

@gtandersen I'm passing you the baton for ideas on how to actually make the "username" identity stand out, currently I just have it with a red highlight the same as the "Email not validated".. however I think it should probably be a solid border, or a different shade or something?

TODO: Integration + unit tests for profiles

[castaway]

New thought: Don't highlight the identity on the main page listing, instead, where the "delete" box would appear (which it doesnt cos you cant delete it), add an explanation?