A unique Statement ID is needed for the edit API call to create a new statement.
This is known for existing statements but must be generated when adding new ones.

• Add new file with export function to Generate Global Unique Identifier (GUID)
• Make imageMediaId a public property for ParticipationManager (access needed for generating statement ID)
  • populateMetaData() and populateStructuredData() also changed to public methods for easy access to this.imageMediaId
• Construct Statement ID from Media ID & GUID