This allows to set the background color without limiting the content

Since sections in dynamic mode require the "contents" display setting
the background color setting must be outsourced.
This way scroll bars are avoided.

Use the status of each element

* Use IntersectionDetector for intersectionDetection directive
* remove unnecessary input 'index' from page component

* Take over tasks of `UnitStateComponent`
* Manage property `unitStateElementCode`
* Removing the passing of the property `unitStateElementCode` by
the components

* `UnitState.dataparts` has property `elementCodes` property, which
stores status, value and id for FormElement
* When building a unit, the stored value is assigned to the element
when it is initiated
* Removed `UnitState.dataparts.pages`
* Removed methods initPages and addStoredValues

Refactor styles for elements and element overlays to achieve stretching
of dynamic sections when text areas are resized

* undo setting overflow hidden for sections
* set display of `ElementOverflow` to block

In the past, the page index could be set by button click and after
scrolling, which led to unwanted side effects

To center the content of the player, the dimensions of all pages are
calculated.

* Move two different intersection detections from
`scroll-index.directive` and `section.component` to
`intersection-detection.directive`

* Fix bug for small pages
* Add functionality for tabbed pages
* Use layoutContainer as container for intersection detection
* Rename properties and methods