#449

- position
- label
- icon

- Replace throwing Errors with InstantiationErors in unit, page and
  section in strictInstantiation mode

- There is a page navigation only for not always visible pages
- Fix initialization of the button's action parameter

Also unit defintion version to 3.10.0

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

- text field simple
- toggle button

- Set the duration of highlighting anchors to 15 seconds
- Disable simultaneous highlighting of anchors

- When the height of the child elements of a cloze element is increased,
they all now grow out of their center

Read-only math fields are displayed without borders

- Add own line height style to error message to exclude it
- Add missing semicolons to styles