fixes bug 1082075

remove the page-bg image in favor of a flat color. white is boring, so instead
we can use the aggregate color of the former background image
flatten the UI, square up those shoulders

fixes bug 1087275

remove most gradient images from the UI, square up rounded panel corners,
remove some borders that were redundant and rely entirely on drop shadow
instead. Tweak some panels and add a title where appropriate.
Merge pull request #2443 from lonnen/1087275-freshen-up

1087275 freshen up