Issue #256 - Fixes issue with RestAuthFilter

* Some request made when importing a spreadsheet use the same
  query parameter (e.g. questionId), the code was only building
  the querystring for calculating the hash
* In the applet code, we "url encode" all parameters except ths `ts`
  to match the version in the RestAuthFilter
* The RawDataImportRequest needs to be able to handle url encoded
  dates