Cloze elements are displayed inline and have no way to show a label.

Now manages height and width by itself. So no overlay div is needed in 
the cloze component.

- Now only has a variable 'document'. This holds the HTML representation
  in an object. This object is enriched with element models.
- Because the the TextEditor extension can neither create multiple
  element instances nor use the IDService to generate their IDs, this
  has to be done afterwards. See ClozeParser.
- The cloze element has rather extensive compatibility handling because
  cloze elements used to save an actual HTML representation. This has to
  be transformed to JSON/object. Therefore we replace the old backslash-
  markers with custom HTML tags. The editor object does this
  transformation. It needs some custom extensions to recognize (and
  don't remove) the HTML tags though.
- Cloze now shows a placeholder text when empty
- The cloze component needs a small pipe to extract text formatting
  options from the paragraph parts.
- For getting the child elements for the player the models have to be
  extracted from the somewhat complex (JSON)document.
- Added some rudimentary interfaces for the TextEditor document format.
- Removed the old ClozePart interface. This is quasi part of the new
  interfaces.

- Give proper name
- Fix variable names
- Fix deprecated methods

This is for the different use saces of a simple text element and a cloze 
element. The latter needs more inputs for child elements and also return 
JSON instead of HTML.

The NodeViews are for the TextEditor to render Angular components, which
now serve as preview instead of the old backslash escaped characters.

All extensions are now placed in a specialized directory. Except the
NodeView stuff which is kept together.

Was missing the actual change of the variable.

Define an offset for textarea or textfield during initialization.
This prevents error messages from the linter.

Show warning messages of input fields at event 'NavigationDenied' only
if reason "responsesIncomplete" is sent

- Map value between unit state and element model
- Takes over methods that were previously present in element container
- Gets and holds a list for mapping drop list elements

This makes the list not collapse when used in dynamic context.

Those are wanted by the product owner.

Also improve tooltips.

- Fix reading values from combinedProperties object. This object has the
needed property in its root.
- Don't show alignment buttons in dynamic mode
- Make the small input fields a little wider so the placeholder text
does not overflow, when there is no valid value to show. This may happen
when multiple elements are selected, which have differing values.

- Move the method to the unit service, so the proper 
updateElementProperty method can be used.
- Also improve the logic, reducing variables.

Only select the element component when it is not already selected. This 
prevents delesecting elements which have been multiselected.

This prevents the section from being placed in front of elements
with negative z-index

This complicates styling and is somewhat useless as the border can also 
be removed by setting the border-width to 0.

Elements are supposed to be centred when this setting is used. Since it 
is the same CSS for almost all element components it is put into global 
styles.

Missing components: video, spelling.

Better logical order with featrures first and bugfixes last.

This reverts commit 87534c53.