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

- text field simple
- toggle button

(The array reference must not be destroyed)

#405

#381

#409

- Add cdk scrolling strategy to keyboard that brings overlays to
scrolling

Drop lists that allow only one element but are not used in cloze texts
display their elements right-aligned

- Add left and right padding for input field

- When the height of the child elements of a cloze element is increased,
they all now grow out of their center

Read-only math fields are displayed without borders

HTML labels can cause errors in the Test Center for units in XML format.

- Show the error message only after the math field has been touched
- Add styles for error message

Since buttons can now act as switches for text-element highlighting, it 
is no longer exclusively used for navigation purposes.

- Mainly highlight border and moving elements.
- Centerpiece is: line-height: 130%;
  Don't know why or how but it works okay.

- Extra span element around cloze child elements served no visible 
purpose. It also makes sense that an inline div is not inside of a span, 
which is meant for text.
- CSS rules were overengineered and in part shadowed (and thereby 
pointless) by element styles from the template.
This is also in preparation for the DropList styling overhaul.

- Add own line height style to error message to exclude it
- Add missing semicolons to styles

Rules for when drop is allowed have been fixed. It is quite complicated 
and therefore a lot of explanatory comments are added.

- improved translation
- add example file

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.

Allows DropListvalueObjects which have this setting to be replaced in
lists which only allow onlyOneItem. When this switch is set, the class
sets the other 2 internal values
(originListID?: string; originListIndex) itself. Those can not be seen
nor changed from outside.

Also refactoring in lots of places around droplists. Better names, 
cleaner structure, comments.

#305