Use ng-content for actual media element.

Player, Posiiton, Styling

- Expand the list of elements zo sanitize to
['text-field', 'text-area', 'text-field-simple', 'spell-correct']
- Rename sanitize method
- Change expectations in tests

- Improve tests
- Change log level logic
- change default log level

Move duplicateElement to it's own method to be used when duplicating 
elements or sections.

'text-field' and 'drop-list' now need '-simple' suffix.

- Disable explicit any rule, because here the native interface of
'window.console' uses 'any[]'

- default log level is 1 (logs are not displayed,
but info, warn and error)
- uses its own logging module
- add path to logging module in tsconfig

Use private methods
Define all messages as properties

Show accordion with expansion-panels instead of tabs.
This way elements can be grouped logically.