This is ised to flatten objects for the proerties panel.

The change of moving some properties to sub objects broke the creation 
of the combinedProperties object, which can't deal with nested objects. 
To circumvent that all elements are now flattened before being combined.
The connected property panels now again look for the properties on the 
element itself and not in sub-objects.

If the property is set, the video will be scaled as far as its
container (static element or grid) allows, otherwise only up to its
maximum native size.

If the property is set, the image will be scaled as far as its
container (static element or grid) allows, otherwise only up to its
maximum native size.

When the magnifier was moved to the right of an image, there was a
possibility that a scroll bar would flare up, depending on the size
of the image. By subtracting the frame width of the magnifier the error
is fixed.

- Dnd values now have a special type that has an ID, a string and
  another string for an image path.
- A new dialog exists for editing thoe options. Similarly to the likert
  header.

Use verona-module-metadata.json to define json meta data in html header

- Fix the name to not have redundant 'component' suffix
- Move template to its own file

Broke during the refactoring of the element models. Now correctly uses 
the positionProps field.

Also improve variable naming.

This is the same hack used in the editor for overlay elements. Here 
applied to the actual dnd elements seen in the player.

Explanation: The cursor can not be applied to the dragged elements as it 
is not positioned (at least that is my understanding). The workaround is 
to style the body (cursor) while anything is being dragged.

If the virtual keyboard with numbers (or with numbers and operators) is
used, input via the normal keyboard is also restricted to these
characters.

It is meant to be used as inline positioned (sub) element. Therefore it 
has not postioning information and less property options than the normal 
drop list. Similar to the simple text field.

MatButtonModule is used in all projects!

The interaction can now be turned off without hiding the button.

If maxRuns at minRuns had the same value, the valid state of an audio
could not be set. Therefore no event was sent to other audios and videos

The latest changes to the events for the control bar have so far been
implemented only for the audio component

This helps to find the asset path for images
when they are imported from the js context

The problem being solved is that compound-sub-elements must not have
all the properties other elements have. For exampe positioning info.
Sub-Elements are positioned inline. To avoid having similar class
inheritance structures for positioned and inline elements, we use
interface. Positioning is done via interface and is therefore optional.

Those optional properties are kept in an object in a variable. This
allows to hide specifics from element classes and removes the need to
initialize all the fields in every class using the interface.
The elements mostly care about their own specific properties anyway.

The same technique is used for font and surface elements. Here we also
don't want to initialize all the styles in every class.

Changing values of element properties works like before. Just set the
property as if it would be a direkt prop of the element. The element
itself puts the value in the currect sub-object (positioningProps,
fontProps etc).

For reading the values there is a similar method, but it is not used
anywhere by now. Since the properties panel operates on the raw values
anyway (refer CombinedProperties) and for element components this would
mean calling a function in the template, which caused change detection
to run the function very often and is therefore bad practice.

Additional notes and refactorings:
- Restructure all files in common. UIElements in the same folder etc.
- Move all interfaces to the UIElement file. This avoids circular
  imports, which would be needed to allow PositionedElement to extend
  UIElement.
- Interface initializers also handle reading values in the old form.
- Add PositionedElement for use in canvas overlays. This is a UIElement
  with guaranteed postionProps.
- Don't export all Material packages from common, only the ones
  used in player and editor. The rest is only used in common and
  does not need to be exported.

This is a native input element which is used in cloze elements. Here 
(sub)elements need to be positioned inline, which is hard to do with 
material components.

Also add a method to all form elements to set their form value, which is 
now only used by the simple text field but may be useful for other 
elements, which don't integrate in material form fields.