Merge the `unitDefinition` with the `unitState.dataParts` to insert the
saved values

Required to decide whether the `section` or `element` should be inserted
or appended to its `formArray`

Required after changes in element components
(commit: 9e3c0613)

* Remove workaround with `Promise.resolve().then(() => ...`
* Use `changeDetectorRef.detectChanges()` after updating the validators

Make the initialization consistent

Getter work like functions and are executed every time Angular change
detection runs.

* Since always visible pages are removed from the order, form
arrays must be rearranged
* Refactor getter as properties in `PlayerStateComponent`. Getter
work like functions and are executed every time Angular change
detection runs.

* Create `FormGroups` without ids
* Add `FormArray` for elements

* Add section array to the form groups of the pages
* Remove unnecessary component factory from `SectionComponent`

* Add specific translation file for editor in assets/i18n
* Add first translations for toolbar

Refactor some translations

more information about [ngx-translate](https://github.com/ngx-translate/core)

In addition to the scrollable pages, units can also have one page that
is always visible.

Use `massageService` of common project.

* Move setting of validators from `FormElementComponent` to
`ValidationMessageComponent`
* Add validators and warnings to `ValidationMessageComponent`
* Move subscriptions for form controls and their validators from
`PageComponent` to `FormComponent`

* Register `PageComponent` as child formGroup, so that values for
any page can be sent to the host.
* Register formControls as controls of the page

`PlayerStateComponent` encapsulates information about the status of the
player.

Also refactor a lot of stuff belonging to this:
- You can edit the default values via properties panel
- All elements now again have a common parent directive. form elements
have a special parent for forms.

Move specific form functionality from `AppComponent` to a new
`FormComponent` to make the code cleaner

* Add verona interfaces to ensure type-safe communication with host
* To use the verona interfaces refactor the verona services

* Implement `VeronaSubscriptionService` to subscribe to messages from
the host of the player
* Implement `VeronaPostService` to post messages to the host of
the player
* Implement `NativeEventService` to subscribe to events like 'scroll',
'blur' and 'focus'
* Remove js code from wrapper index.html. It is no longer needed.

* When creating components for each element a
`ValidationMessageComponent` is also generated dynamically
* Prepare usage of default values for form elements
* Add `form.ts` for form specific interfaces
* Rename some variables and properties

* Only elements which has to be registered by the player's form inherit
from `FormElementComponent`
* Element components use their specific `elementModel`
* Rename file for `FormElementComponent`

Move all player components to component folder but `AppComponent`
Improve naming of variables