drag and drop from sidebar implementation

This will be valid for mechanisms and compositions

reference to this

http://projectstorm.cloud/react-diagrams/?path=/story/advanced-usage--drag-and-drop

Start by reviewing the issue description and the referenced React Diagrams drag-and-drop example. Identify how the sidebar represents mechanisms and compositions and determine the expected drag-and-drop behavior before locating the relevant implementation and tests. Done means both item types can be dragged from the sidebar as described.

Written by the indexing model from the issue text.