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

#547

- Use own StateVariableStateService which uses the same new base class
as UnitStateService

- Only elements with this property are considered in the player when
determining the presentation state
- Add the registration of CompoundElements at the UnitStateservice
- Fix visibility handling of section with simple rules

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

- Refactor directive

- Basic implementation

- Using scrollIntoView with target 'center' was not always reliable
  especially in FF

SectionVisibilityHandlingDirective now controls the visibility of
sections that depend on an audio or video

This way elements can handle their logic themselves without having to
rely on outside utility classes.

Also restructure files in common in a more logical way.

Change import paths of CommonModule files in editor and player

to ensure that a section that is not displayed has no dimensions

Sections use the mediaStatusChanged event, which is also used to map the
interdependence of media elements

This removes all the classes and goes back to simple interfaces for
unit, pages etc and all elements. This makes creating them easier and
cleaner.
Things like specific needs when setting element properties and most
importantly compatibility handling is done by a special service module,
that knows all the elements and how to repair old their potentially
outdated definitions.

This is done according to the Angular best practices and minimizes
namespace collisions when using other packages which might use the same
selectors.

Technically the selectors are not even becessary since we use an Angular
component factory to create element components but it is still useful
for the DOM element naming, for debugging purposes for example.

Use the status of each element

* Add IntersectionService
* Add CompoundElementComponent as parent for LikertComponent
* Inject ElementRef to common ElementComponent
* Rename players' ElementComponent to ElementContainerComponent

* Remove FormService Injection
* Move FormService and form types to player
* Move interface ValueChangeElement to uI-element.ts
* Use interface InputElementValue instead of
string | number | boolean | null