Replacing the internal script loader for app manifest scripts

Per discussion in #11 and specifically [this comment](https://github.com/OpenF2/F2/issues/11#issuecomment-21193695), we're replacing the internal app manifest script loading mechanism. The current version uses `jQuery.ajax` and developers cannot effectively debug issues with F2 app dependencies loaded into the container. By replacing this with `document.createElement('script')` enables better debugging and removes the jQuery proxy.