- Remove all Roboto files

Since there is just one font, this setting can be safely ignored. This 
is easier than sanitizing all elements.

#533
- Remove unnecessary and wrong setting of underline property

#521

- Reformat styles

- If this property is set, the input of more characters than specified
in maxLength is prevented
- It also prevents the insertion of text.

- Reduce redundant code
- Prepare implementation of input limitations

- Remove prefix 'on'

This way elements can handle their logic themselves without having to
rely on outside utility classes.

Also restructure files in common in a more logical way.

Rename KeyboardComponent to KeypadComponent
Rename KeyboardService to KeypadService
Split LayoutComponent into LayoutPlayerComponent and
LayoutPagesComponent
Prepare the introduction of an additional keyboard

Disable spelling correction as well
- Use the attributes autocapitalize, autocorrect, spellcheck
- Replace [value]="elementModel.value" with
value="{{elementModel.value}}" to prevent lint errors

belongs to commit #14dcebca

- 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.

This helps to divide the code of the element container into smaller
meaningful units.
In addition, each element can be given its own form group.

- Unify font and surface props
- Use intersection type for additional properties
- Also rework editor props panel to properly create the combined 
properties recursively, passing the results to its child panel (tabs).
New algorithm works without lodash, therefore the package is removed.

This removes all the classes and goes back to simple interfaces for
unit, pages etc and all elements. This makes creating them easier and
cleaner.
Things like specific needs when setting element properties and most
importantly compatibility handling is done by a special service module,
that knows all the elements and how to repair old their potentially
outdated definitions.

Remove the wrapper divs in each element component and add the
'fixed-size-content-wrapper' class to the element overlays
of player and editor

The previous solution, which uses a top position of 50%, did not work on
iPad

This is done according to the Angular best practices and minimizes
namespace collisions when using other packages which might use the same
selectors.

Technically the selectors are not even becessary since we use an Angular
component factory to create element components but it is still useful
for the DOM element naming, for debugging purposes for example.

- Use the same font properties for input element and button element
- Change cross out behaviour. The button now behaves as
toggle button and sets the focus to the input element only when it is
crossed through.

- Remove function call in template
- Init value with elementModel.value
- Set readonly and disabled properties in template and remove OnInit
- Compact code