Advanced search

This adds the advanced search feature is it is provided from the `blacklight_advanced_search` gem. One of the commits overrides the index view so that the navbar from the application can be added to the advanced search page. 

@rez7 Right now the link to the advanced search page is just a text link under the search bar to the page at /advanced. This should be something that we ask about in the questions for the beta relaease. i.e. should this be displayed in some other way or location (in the links bar?).

Something else that I'm not sure what we should do about is the section at the bottom of /advanced that says "AND have these attributes". This is something that comes from the default advanced search, but I'm not sure what it is supposed to be doing, and I'm not usre that other uses will know what to do with it either.