Add theme asset dirs to config.assets.path.
Update image references to use asset image_tag calls
Remove obsolete example file.
Update stylesheet inclusion for asset pipeline.

Some @imports are superceded by the application.css manifest. For the
blueprint imports, use the solution suggested at

http://stackoverflow.com/questions/7769799/configuring-blueprint-in-rails-3-1

for including the stylesheets in the relevant context.
Convert stylesheets to scss

So that we can use image-url
Fix path.

Seems clearer and more robust to specify it relative to rails root.