The height of an empty droplist can't be calculated on ios 14
because it's in a flex container

#229

- Use `inputmode` 'none' to hide the virtual keyboard of the os
- Use DeviceService to detect if the player is running
on a mobile device

verticalButtonAlignment is the new property for likert rows, which tells 
the actual radio button to either be at the top or in the middle.

Also rename LikertColumn to ColumnHeader, since it is not exclusively 
used by likert.

- A new new editor component has been created for this, which has a
reduced interface and produces span-elements instead of paragraphs.
- Since the created HTML (span with CSS) is regarded as potentially
harmful it needs to be sanitized. For element components the sanitizer
is put in the abstract parent element-component-directive.

This allows showing the contained text in multiple columns.

There were several issues with it's properties, which could not be 
changed.
Now it is properly initialized and prop change get actually handled.

Rename KeyboardComponent to KeypadComponent
Rename KeyboardService to KeypadService
Split LayoutComponent into LayoutPlayerComponent and
LayoutPagesComponent
Prepare the introduction of an additional keyboard

Replace custom pointer events with native pointer events

Instead, use Textfied component with the property isClozeChild

Remove duplicate code

Disable spelling correction as well
- Use the attributes autocapitalize, autocorrect, spellcheck
- Replace [value]="elementModel.value" with
value="{{elementModel.value}}" to prevent lint errors

belongs to commit #14dcebca

- Use the attributes autocapitalize, autocorrect, spellcheck
- Replace [value]="elementModel.value" with
value="{{elementModel.value}}" to prevent lint errors

- Units and element are now built via the factory. This ensures only the
  wanted properties are present. All others are discarded.
- Since the sanatizer is supposed to check the unit defintion version
  it is used by player and editor and therefore put in common.
  This in turn makes it necessary to put the JSON resolver settings
  in the root-TSConfig file.
- Renamed a couple of properties to have clearer names.

Remove manipulations from elementModel
- Refactor drop list component
- Use of initial values for audio and video playback time

Defining the validators not in the elements anymore, but when creating
the forms

This helps to divide the code of the element container into smaller
meaningful units.
In addition, each element can be given its own form group.

This makes for cleaner imports.

- Unify font and surface props
- Use intersection type for additional properties
- Also rework editor props panel to properly create the combined 
properties recursively, passing the results to its child panel (tabs).
New algorithm works without lodash, therefore the package is removed.

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.