DragNDrop, Bugfixes

What's Changed

• [DragNDrop] add drag&drop mechanic by @elija-feigl in #21
• We now check if _modelVirtualHelix exists before returning its number. This may help avoid a frequent crash.

New Contributors

• @elija-feigl made their first contribution in #21

Full Changelog: v2.4.3...v2.4.4