Fixed view and JS to be compatible with jQuery 1.8

Related to https://github.com/stephenmcd/mezzanine/issues/735.

In jQuery versions before 1.8, if the value of a POST variable was null, jQuery posted 'null' to the server.

In jQuery 1.8 and higher, jQuery posts an empty string for a null value. (See jquery/jquery#714)

Changed js to put null in quotes and changed views to accept an empty string as well as a null.