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

- Prepare usage in editor
- Remove test from ScrollPagePipe, because the call to "new Page" expected
  the initialization of GeometryComponent

- Remove css margins of floating keypad

- A floating keypad is generated inside a div with the class
  'cdk-overlay-pane'. Now the position of this div is updated when
  dragging the keypad.

- Add spans with 'nbsp;' to images to be able to align drop lists of
  cloze elements with images to the baseline.

- This prevents the cursor to be set to the upper left corner of the
  preview image

- Allow put back
- check if to replace item can be moved elsewhere. this is only possible 
if it is not in it's origin.

Now checks again if the source list was a copy list and discards the 
item if so.

Hold the replaced item while doing the actual transfer and add it to 
it's origin afterward. This way it can not be transfered after being 
moved back.

- list-item is styled as placeholder
- placeholder has no dimensions

If the placeholder or the item is hidden
the other one leaves the list when dragged