Logo overlap fix

Change to CSS file.  this issue is known and documented in SO:

http://stackoverflow.com/questions/11124777/twitter-bootstrap-navbar-fixed-top-overlapping-site

The CSS seems to be hardcoded to the height of the banner img so this is something that could potentially go wrong in the future if the banner changes.  If some kind of CMS is integrated, will need to be more dynamic obviously.

Staged in the usual place-- check the scrum or im.