#662

- Remove all Roboto files

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

- Fix typo in css classname

- Basic implementation

The property vertical-align is interpreted differently by Chrome based
browsers, so a special webkit value is needed to override the value. The
browser specific value is used last, so it is used by browsers which can
interpret it.
#414

Uses external software 'MathLive'.

Distpacker issues with mathlive have been solved in a custom 
distpacker.ts in scripts-folder. This is now used instead of the 
distpacker from the npm package.

Red background looks really bad, so we just adjust the border color.

Just called from the editor, before creating the Unit instance.
It goes through all IDs and checks for duplicates. If found it generates 
a new one and shows the prompt.

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

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

The line-height setting on the before and after selectors are so the 
quote does not reserve space.

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.

This creates a blockquote-element, which is styled globally with 
specific quotes and alignment.

- Remove grab cursor from the canvas as it is no longer draggable (was
  in an earlier version)
- Fix element visual overlaying the resize element. Now the actual
  element is hidden, while the resize is going on.

Element cursor are changed so that there is a 'grab' cursor on hover
and a 'grabbing' cursor while active (clicked but not dragged yet)
and while dragging.
The resize cursor always stays the same, as there is not alternative
active curser (like grab/grabbing) for this.

On the dynamic overlay the curser cannot be set while the element
is being dragged. I assume it is because of 'relative' positioning.
The element is taken out of the DOM and pointer events don't work,
including cursors. This is why the body needs to be cursor-styled.
Cursors are set dynamically in the component via CSS class.
When dragging starts it is set and removed when it ends.

Use global styles and remove unecessary styling commands. The dialog 
window will mostly size itself.

And avoid global styling.

This is rather hard to implement via HTML inline style attributes. So we 
do it the classic way.
Could be reviewed, when that feature is implemented in TipTap:
https://github.com/ueberdosis/tiptap/issues/1514.

They are now modified via menu at the section and no longer via props 
panel.

Use global style for droplist cursor.

- ... mostly for dynamic positioning
- Refactor reordering of sections. They can now be moved by small
buttons to the side, which appear when hovering. The section edit mode
is no longer available. -> KISS
- Removed all toolbars. The props can now be set via the props panel,
which now has sections for pages, sections and elements. This is to have
more vertical space available for editing the unit.
- Sections can now (only) be added via the toolbox panel, where the
second tab is now exclusively for sections. Future templates are
supposed to be whole sections, which can also be added from there.
- Refactor CSS layouting (flex and co) to have better handling of
vertically growing page (via sections)
- Some preparation for an upcoming overhaul of selection stuff
(again :))

Somewhat messy because of more nested droplists and a handler triggering 
every pixel. But the best I can do for now. May revisit later.

Stronger then warning.

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.