Default form to custom form transfer of data fields

[aoduor]

"If a user opens up an existing report as a default form, and changes the dropdown to a custom form that was created, all of the additional custom data fields should now display and be capable of being edited. For example, if a user without an account entered a report, and then a registered user associated with the incident response wants to move the form to a custom form that had been created, they should be able to do so in the edit process. Currently you can switch back and forth between the default form and custom forms but the additional data fields don't transfer over." - Justin

[bodacea]

I've added this to the V3 features wishlist at https://phabricator.ushahidi.com/T598; please feel free to continue working on this for V2.