- remove 'none'

#662

#643

Helps to mark text on windows mobile, because the contextmenu hides the
handles bars of the selection

- Remove all Roboto files

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

#513

- Can also be used with other elements

Octal characters are deprecated and don't work anymore. This solution 
uses an empty string over the whole line.

#502

The extension is needed to define text areas in the rich text editor
and make them available for the button component

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.

This allows showing the contained text in multiple columns.

Replace custom pointer events with native pointer events

- 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.

Remove manipulations from elementModel
- Refactor drop list component
- Use of initial values for audio and video playback time

Defining the validators not in the elements anymore, but when creating
the forms

- 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outdated definitions.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.

- Remove element as parameter

- Implement marking buttons as toggle buttons

- Check if the selection refers to the content of the text component

This disables the possibility of nested markers

Elements are supposed to be centred when this setting is used. Since it 
is the same CSS for almost all element components it is put into global 
styles.

Missing components: video, spelling.