Force ajax dataType to html

This fixes the "html.replace is not a function" error.

`utility.storePageIn` requires the 3rd parameter to be a jQuery or a string. But, on line ~452, the ajax success callback caller sometimes passes an XMLDocument object (instead of an HTML string) to the `html` parameter in the callback. This is passed to `ulitity.storePageIn` which expects a jQuery or a string.

This change forces the request result to be an HTML string, instead of the default auto-guessing.