Add styles for bar and buttons

to avoid name collision.

This was an early draft and unused. Will be reintroduced in a proper 
form later.

* Delete validation message component
* Use instead `mat-error` inside element components to take advantage
 of `mat-input-field`
* Add get validators method to each form element component
* Display validation messages via `error-transform` pipe

Since the material elements don't give a way of applying the background 
color, a hack is needed to get the internal elements and apply the 
style.

Directive to be able to do it for text field and text area.

The urls must be declared as trusted to be accepted by the application.

Also some small improvements to variable naming and file structure.

#23

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

more information about [ngx-translate](https://github.com/ngx-translate/core)

- Service is used by the editor exclusively so definition in
local app.module.

- Edit dialogs triggered via double click on drag overlay
- Unit Service now defines a default edit dialog for elements. For now
label or text if available.

Since this does not label anything but instead is meant for (longer)
texts.

* Introduce `FormService` to provide communication between
element components and form
* Add `ngModelChange` and `formControl` to
some element components. This functionality is not used by
the editor

This defines the elements priority when stacking elements on the canvas. 
Directly maps to the CSS property.

Also show tooltip on the input to explain what it is for.

The extra styling via panelClass needs CSS definition in local project, 
so can not be set by the Service itself but relies on local CSS rules.