CSS optimizations

* Match the styles of the breadcrumbs and the top nav by replacing the image used on top nav with an rgba equivalent (and thus optimizing network).

* Search block form change proposal for better positioning and aesthetics.
Put it at the same height as the breadcrumbs.

![screenshot_saladeprensa_fortaleza_06082013](https://f.cloud.github.com/assets/4642358/627982/276f158a-d06f-11e2-8011-b56e457cb31a.jpg)