- Add translations for operators
- Improve and extend the evaluation of visibility rules

Also restructure files containing interfaces.

Toolbar is a single word, therefore any capitalized letters are errors. 
No need to sanitize, since this was broken anyway.

#384

- allowReplacement (moved from element to list prop)
- originList and Index are non-optional (means placeholders have to be 
used sometimes)
- Re-introduced the dict of all DropListComponents. This is the only way 
I have found to get a reference to a DropListComponent by ID. This is 
needed for returning to origin. Origin is not actually part of the 
transaction and needs to be fetched from somewhere else. Hence the dict.

- Console statements still present for debugging.

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

- Add cdk scrolling strategy to keyboard that brings overlays to
scrolling

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

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.

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

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

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

Reads file as base64.

Also rework the GeoGebra dialog to close automatically when a valid 
definition is available, either through pasting or file upload.

- Part of the properties panel for every element (like delete and 
duplicate)
- This allows interacting with elements, generating events and inpect 
their usage. Usually this is unwanted since it might interfere with 
dragging the overlay, but sometimes you want to get a feel for the 
element or check it's contents (GeoGebra for example)

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

- A HotspotImage has an image and divs placed on it, which are used
as hotspots
- Inherits from FormElementComponent, which is why the hotspots are kept
  as a list in the value property.
- Can be validated as required and uses its own custom validator

Top and bottom were mixed up.

#291

- add translations

Aslo create new props panel component and move border stylings to 
separate fieldset (wihtin the styling tab).

#291

Add new parameter 'itemsPerRow'. This limits the grid columns used, 
making items move to the next row if overextending.

Also simplify component structure.