Switch to using UUIDs in XSNs to refer to Forms

Form Entry XSNs rely on Form IDs embedded in the content of the cab file in order to ensure the "Upload XSN" mechanism works. Since Sync Module and Metadata Sharing Module ignore IDs and focus on UUIDs, allowing the API to auto-generate IDs for new content, an XSN file downloaded from one server cannot necessarily be uploaded to another server.

We need to modify the XSN (and potentially all other code that references Forms by ID) so Forms can be recognized by UUID.