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

This reverts commit f90bcc5b
Target installation seems not to support this Verona Api version yet

Mathlive package requires some more space.

Uses external software 'MathLive'.

Distpacker issues with mathlive have been solved in a custom 
distpacker.ts in scripts-folder. This is now used instead of the 
distpacker from the npm package.

Allows DropListvalueObjects which have this setting to be replaced in
lists which only allow onlyOneItem. When this switch is set, the class
sets the other 2 internal values
(originListID?: string; originListIndex) itself. Those can not be seen
nor changed from outside.

Also refactoring in lots of places around droplists. Better names, 
cleaner structure, comments.

#305

Lists with this setting delete dropped value objects. This allows 
putting items back.
(Only makes sense when used with copyOnDrop. Otherwise there can not be 
duplicate value IDs).

Also improve constructor value checks to correctly handle nullish 
booleans.

#281

- This allows to reset Geogebra to the state defined in the unit
definition

- Convert player release notes to markdown file

This was necessary because the new text selection action of the button
is not a navigation.

- Areas are marked with the surrounding 'aspect-anchor' tag

The extension is needed to define text areas in the rich text editor
and make them available for the button component

This way images can't be drag-and-dropped into droplist elements.
Also avoids confusion about what is draggable on a page.

- If this property is set, the input of more characters than specified
in maxLength is prevented
- It also prevents the insertion of text.

- Reduce redundant code
- Prepare implementation of input limitations

The updateListener does not detect all changes inside a GeoGebra element

#309

The API has been updated and some commands and fields are removed. They 
are kept in for compatibility.