 Fixing further PHP warnings
 Added single select field
 Maintainable and customizable supporters
 Allow separate email texts per supporter
 Preventing the submission of proposals for expired calls with 3 hours cooling-off period
 Keep error navigation after submit attempt
 Allow bulk decline of proposals
 Significant reduction of PDF export file size
 Allow reset of the revision status
 Consideration of deleted proposals for the signature counter
 Various minor fixes