gridColumnStart to gridColumn, for example.

This can be enabled for TextFields and TextAreas and shows a keyboard
at the bottom of the screen. This does NOT set the field to read-only
which is probably wanted in a situation where the system keyboard is not
to be used. For flexibility purposes it is not implicitly set and needs
to be set manually. The same goes for other input assistance settings,
which should not be used in addition to the keyboard but it is allowed.

The keyboard has an extra switch to additionally show french special
characters.

This makes newly created elements appear next to each other instead of 
on top.

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

gridColumnStart: number;
gridColumnEnd: number;
gridRowStart: number;
gridRowEnd: number;

becomes

gridColumn: number;
gridColumnRange: number;
gridRow: number;
gridRowRange: number;

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

The unit definition now has 2 meta-fields: 'type' and 'version'.
The former has the fixed value of 'aspect-unit-definition'.
The latters contains the version without any prefixes, i.e. '1.2.3'.

The sanatizer tries to read the versions of older formats as well and
uses the found version. This is important since the handlePlusOne
method must only run of a specific version (in the old format).

The sanatizer no longer shows any messages and therefore does not need
the MessageService anymore. The information about whether sanatization
happened or not is returned as second parameter for those that are
interested. The editor is, the player is not.

The editor API service now constructs the 'unitDefinitionType'
parameter from both values, resulting in something like
'aspect-unit-definition@1.2.3'.

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

Replace the direct method calls in media player components with events.
For this purpose, expand the inputs of the media player components that
are defined in the ElementMediaPlayerGroupComponent.

- 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.

Since the array of 'ClozeElements' can be empty, it must be checked

The factory was ignoring the src parameter, which is set before by the 
UnitService.

Instead, use :host in conjunction with ::deep

- 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.