Move required styles and classes to the overlays of player and editor

- Use fixedSize always together with dynamicPositioning!
- Rename css class 'center-content' to 'fixed-size-element'
'fixed-size-element' ensures that the content does not overflow.

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

Note that autostart of audios and videos does not work for tablets

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

The former outline was always displayed square on the iPad

Ignore grid sizes when dynamic mode is active.
This has the added benefit of adding some actual dynamicality to the 
grid in the editor.

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.

The 2 different radio button variants (with and without images) are now 
hidden behind one radio button entry. Functionally everything else works 
the same.
Also move CSS to it's own file.

The package was not a proper ECMA Script package and therefore can not 
be tree shaken properly and would unnecessarily increase the package 
size.

- Simplified the code logic. Verification is done once in the beginning 
and not on every element.
- Now uses semver to verify and compare version strings

Now shows an error message and continues with an empty unit.

This may destroy alignment of inputs and produce unwanted scrollbars.

It is better to hide that abstraction in the unit service.

Better solution without an extra variable.

- This improves scroll snap behaviour
- Set background color of page
- Interpret the margin of a page as padding. What it really is