Account page style and usability fixes

This ticket is a general style clean-up of the Accounts page. Namely:

- general CSS style fixes
- sidebar styles now consistent with other pages in app
- focus is placed on first text box on page when page load (N.B.
autofocus wouldn’t work consistently, hence the JS)
- "Databases" left nav item no longer selected

*** Please note: the Create Admins page is still having it's text cut
off. This will be fixed once PR #123 has been merged. ***

Closes COUCHDB-2417