Prevent duplicate docs in cart and filter search accordingly

In a future version, we'll probably want to have docs that have already
been added to the cart show up in the search results, but styled such
that it's obvious what's going on.
Add charset specification to ajax request.

Firefox automatically adds it, chrome doesn't, the current backend
chokes on it not being present.
Whitespace fix
Merge pull request #2 from TehMillhouse/master

Prevent duplicate docs in cart and filter search accordingly