Add Element Insertion, Re-Ordering and Removal to PropertyGrid IList Editor

[ilexp]

Summary

The current implementation of the PropertyGrid IList editor does not allow to re-order to remove elements. This can get quite annoying and cumbersome in cases where element order matters and an element has to be inserted at some point. It should be possible to...

1. ...insert a new element at index N.
2. ...take an element from index N and insert it at index M.
3. ...remove an element at index N.

Analysis

• This could be solved by introducing left side "element handles" that allow drag-drop operations.
• Movement is solved by drag-drop.
• Removal is solved by introducing a removal button on the handle.
  • Make sure to remove all now redundant delete button usages for this purpose.
• Insetion is solved by introducing an insertion button on the handle.