One as a general label above the table and one for the first column 
heading.

Since this is no proper InputElement separate properties panel inputs 
are used.

#272

- Move props to separate files
- Fix typing

Also improve media element property control layout.

#204

- Add fieldset and reorder fields
- Add dynamic connectedDropLists menu

Components with bigger scope are put to the component root, canvas, 
props panle and new-element-panel.

- Move value input to dropList input group

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.

This makes for smaller more managable components.

This allows showing the contained text in multiple columns.

The text area was mistakenly shown.

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

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.

- 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.

- Use sub components to reduce the size of the templates
- Introduce field sets for input groups like dimensions and position
- Improve logic to determine when to show some fields

All elements which report the selected index are supposed to send an 
index starting with 1 instead of 0. This a special requirement for the 
analysis of answers.

Refactor MathKeyboardComponent to reduce code size

Cloze no longer has a text property and needs a way to open the 
TextEditor.

Now manages it's width and height itself.

Also has some new properties:
- verticalOrientation should be self-explanatory
- dynamicWidth allows the user to set a width manually. The buttons on 
the element automatically stretch to meet the set width (or height).

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

Use a suffix button to activate color picker instead of having an extra 
form field.

Also add direct input for likert line coloring color.

This new setting makes child items space around in a row with line 
break.

Images in vertical alignment now always reserve the whole row and don't 
appear next to each other.

The other  variants are basically the same as filled. The only
difference is the background color, which we are manilupating anyway.
So there is no reason to keep them.

Also for the background color directive different target elements are
needed for the different appearance variants. This is now possible.
As stylings of the old appearance are kept when changing the appearance
the styles need to be removed first.
In the moment the appearance value is changed the component is not
actually changed yet and there we need to wait for another Angular
change detection cycle, via timeout.

Basically a div with border properties as usual.