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 actual unit reference from UnitService instead of a possibly not 
up to date local variable.

The width of a page results from the value for the maximum width plus
twice the value for the spacing

- 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.

belongs to commit #f6668bdd

- 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.

- Verification is task of the common sanitizer
- Remove unnecessary AlertDialog

- Reimplement UnitStateComponent as central point to send the collected
information
- Implement ValidationService to determine the responseStatus of all
forms

This was necessary after the surrounding element container with its
styles and classes was deleted

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.