* When elements receive the focusin event, their status is changed to
`TOUCHED`
* Replace `this.form.valueChanges` subscription with
`this.unitStateService.unitStateElementCodeChanged` subscription

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

* Value and status of all elements are saved
* Move some Methods and Properties from FormService to UnitStateService

* `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

The DOM query is now only done once and nt again everytime the value 
changes.

* Adapts their appearance to mat-form-fields
* Fix coloring of background for checkboxes

Overridden by some child elements (TextField, CheckBox)

* Delete validation message component
* Use instead `mat-error` inside element components to take advantage
 of `mat-input-field`
* Add get validators method to each form element component
* Display validation messages via `error-transform` pipe

Since the material elements don't give a way of applying the background 
color, a hack is needed to get the internal elements and apply the 
style.

Directive to be able to do it for text field and text area.

* Remove unnecessary styles
* Refactor case distinctions
* Improve styles of some elements

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

to prevent unnecessary scroll bars from appearing

This is preliminary and will be reworked in the future.

Consider the available space for width and height
Increase their default heights

to prevent vertical scrollbars when using default values.
* Increase height for TextFieldElement, TextElement and DropdownElement
* Change HTML structure of TextElement

This enables to hightlight parts of the text with colors.

This uses kolkov/angular-editor.

The urls must be declared as trusted to be accepted by the application.

When this is set the page will only be rendered to that width. Otherwise 
100% of the available space is used.

This property should be used when an always visible page is used and 
states the ration of the always visible page to the other pages.

Before it was the index of the option. HTML UI Elements take the actual 
value as parameter anyway so no need to use any index.

The section now always has the same width as the page (minus margin).

Can only be true/false.

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