bugfix + enhancement to support modeladmin
bugfix + enhancement to support modeladmin

Update to allow UserDefinedForm pages to be managed through ModelAdmin.
* Needed to update the ID of the form.
* Bug on the form data serialisation (missing ampersand breaks security token.)
mcccclean/silverstripe-userforms,flamerohr/silverstripe-userforms,sekjal/silverstripe-userforms,dnadesign/silverstripe-userforms,marcokernler/silverstripe-userforms,flamerohr/silverstripe-userforms,souldigital/silverstripe-userforms,martinduparc/silverstripe-userforms,madmatt/silverstripe-userforms,candidasa/silverstripe-userforms,frankmullenger/silverstripe-userforms,candidasa/silverstripe-userforms,sekjal/silverstripe-userforms,marcokernler/silverstripe-userforms,marcokernler/silverstripe-userforms,frankmullenger/silverstripe-userforms,oddnoc/silverstripe-userforms,frankmullenger/silverstripe-userforms,candidasa/silverstripe-userforms,souldigital/silverstripe-userforms,robbyahn/silverstripe-userforms,martinduparc/silverstripe-userforms,flamerohr/silverstripe-userforms,dnadesign/silverstripe-userforms,mcccclean/silverstripe-userforms,souldigital/silverstripe-userforms,oddnoc/silverstripe-userforms,silverstripe/silverstripe-userforms,mcccclean/silverstripe-userforms,robbyahn/silverstripe-userforms,silverstripe/silverstripe-userforms,madmatt/silverstripe-userforms,madmatt/silverstripe-userforms