Updated Search Bar Style

Please note that I don't feel that the search bar needs to be skinned by
users, hence why it is not part of the large css-skinning project. I
also feel that given the PR #416 a new search bar with highlight the new
search functionality.

Updated the look of the search  bar:
+ larger, curved edges
+ changes color when has focus
+ search icon built into search
- removed "Search For" text in lieu of search icon
I'd avoid to hardcode a style in the binary; it may look good in your box, but could appear incoherent under other os/desktop managers. Typically qt makes a good work at faking an os-integrated appearance, it could be nice to create external skin files (who remembers mIRC scripts with custom themes?)