R1:f713fa1fd7ec

Expand "Settings" UI to full-width

Summary:
Depends on D19988. See D19826 for the last UI expansion. I don't have an especially strong product rationale for un-fixed-width'ing Settings since it doesn't suffer from the "mystery meat actions" issues that other fixed-width UIs do, but I like the full-width UI better and the other other fixed-width UIs all (?) have some actual rationale (e.g., large tables, multiple actions on subpanels), so "consistency" is an argument here.

Also rename "account" to…