Also unit defintion version to 3.10.0

The native browser-drag-and-drop does not work in tablets. Therefore 
back to Material which works.
Features are moved over with the exception of replacing items.

- Copy-Lists now always allow putting items back.

- Renew example files
- Update versions and notes

- text field simple
- toggle button

- Set the duration of highlighting anchors to 15 seconds
- Disable simultaneous highlighting of anchors

- 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

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

- Convert player release notes to markdown file

- If this property is set, the input of more characters than specified
in maxLength is prevented
- It also prevents the insertion of text.

- A HotspotImage has an image and divs placed on it, which are used
as hotspots
- Inherits from FormElementComponent, which is why the hotspots are kept
  as a list in the value property.
- Can be validated as required and uses its own custom validator