Added modal view of comparison of up to 3 schools

Notes:
1. For now the comparison view is generated by data held in sessionStorage. The data are culled from the page the user sees and initially stored when the user selects a favorite. (It is removed when the user removes the favorited school.) This method of collecting the data should be changed, but for the most part, as a first pass it works. One exception is that we need to remove the "Add to Favorites" checkbox from the comparison view.

2. I added a section displaying some Favorites info.  It contains a link to compare the favorites, as shown on the moqup. It also lists the schools selected as favorites. (Not shown on the moqup, but it made development much easier, and it seems that  eventually we'd want the user to have access to this data, so I left it in place.)

3. va_files/2012/styles/compare-modal.css was copied from modal.css. It can be cut down significantly or eliminated by folding the two files into one.  many of the rules do not apply, but have not yet been deleted.