Add logolink

Number of confusing things here. The float right code is already on master: https://github.com/mattkiernan/craigstr/blob/master/app/views/layouts/application.html.erb, so you are likely behind master.

Likewise, I requested that the classname be changed to be more meaningful, less style-specific: https://github.com/mattkiernan/craigstr/pull/6#discussion_r19817017

Please rebase then make that change (use a more meaningful class name)