This is now always disallowed when there is only 1 page. There is an 
issue when this is set and further pages are deleted, but this scenario 
should be very rare und non-consequential.

Input element with type number still returns string. Therefore we need 
to convert the value before sedning it to the unit service.
This was causing a bug later when resizing the element on the canvas.

The version is taken from the package.json file and replaced in the 
html.

This stuff is managed via the host (teststudio) and not by the editor 
itself.

Now correctly selects the first section of the page changed to.

Instead of manipulating the page object directly via ngmodel.
This way the unit service may inform the host about changes. Also future 
undo functionality is prepared.

* Fix bug for small pages
* Add functionality for tabbed pages
* Use layoutContainer as container for intersection detection
* Rename properties and methods

Teststudio does not show patch versions.

Unsubscribing, private methods ...

Also some small improvements to variable naming and file structure.

#23

To communicate with the host application.

This allows the API service to send the unit definition to the host.

- Unit service now again takes the elements to be changed as parameter
instead of managing (and even knowing) selections.
- Selections are managed by the appropriate service
- Also using rxjs operators instead of serving observable state as
getter method.

Move `MatDialogModule` from editor to common
Add `AlertDialog` to player

Check whether `unitDefinition` or `unitStateDataType` are undefined is
done within the verify methods