The native browser-drag-and-drop does not work in tablets. Therefore 
back to Material which works.
Features are moved over with the exception of replacing items.

- Copy-Lists now always allow putting items back.

- Renew example files
- Update versions and notes

Rules for when drop is allowed have been fixed. It is quite complicated 
and therefore a lot of explanatory comments are added.

- improved translation
- add example file

- Replace Material Droplist with native HTML events
- Remove simple-drop-list element; Cloze elements now use the normal 
DropList element
- Add example units