Make form controls easier to see

[joemull]

Fixes #365.

Three changes to make this happen:

• Make backgrounds white again, even in blue boxes, since the HTML we get from Django forms is not amenable to Hourglass styling if we try to make a blue background work. This is also more consistent with rich text fields, which are styled by TinyMCE, and it makes the fields more visible in general.
• Remove bottom border (previously a white line)
• Change focus-visible outlnie on inputs (no change to links and buttons) to be a blue line with 2px offset