This is necessary to reset elements like radio button group. We use null 
for that instead of undefined.

The check was in place before to make sure input fields only accept 
valid values (no text in a number field for example). Angular thinks a 
null value is valid so we have to do this extra check. This is now done 
directly in the template before calling the updateModel method.

The outline needs some space outside the element. This space may be more
than the parent has (when the element is positioned right at the edge).
When this happens we simply ignore that 1 pixel space. Everything still
shows correctly.

And avoid global styling.

This way empty paragraphs still produce an empty line.
Not possible to do inline because CSS pseudo classes do not work inline.

This way the color-input element can read the color and show the correct 
preview.

This needs a z-index on the selected section, since the outline collides 
with other sections and is not shown on this side.

Was missing margin at the top.

Put the buttons to the right side instead of in the middle somewhere.

Make radio button and first line of the label (in case there is a line 
break) appear at the same height.

This makes it so that other options appear with strikethrough when one 
is selected.

Other components will follow.

This allows for further marking options on the text, which may be used 
for different purposes.

Since this is built using a grid it does not need dimensions. In fact it 
having dimensions interferes with styling.

For elements which don't have this functionality the workaround is to 
use pointer events and make the elements unclickable.

* Add IntersectionService
* Add CompoundElementComponent as parent for LikertComponent
* Inject ElementRef to common ElementComponent
* Rename players' ElementComponent to ElementContainerComponent

This improves bold text readability.
This has to be done in the actual element, in the TextEditor and on the 
properties panel.

Add 10px margin between label and options.

When the label is empty a smaller input field will be rendered which 
also does not have the label placeholder.

This has been refactored already. Those were not cleaned up properly.

Useful for longer text in textareas and does not hurt short text 
elements (like text-field).

This way the vertical size can be controlled.

Other elements do implement the interface but do nothing with the 
property. This make all the interface handling a lot easier at the cost 
of having useless variables in some contexts.

By clicking anywhere but elements of the side panels.

The outlines where not completely shown when multiple elements were put 
beside one another. Now the selected elements of pulled to the top and 
the outline is visible.