### Tasks
- [x] decide what to do with the remaining content in the original file that have not been integrated for now. It is mainly about the browser usage of mxGraph. This content requires rework. If needed, create a new issue to delay this. #621
- [x] rename the images: some are style prefixed by mx. Decide if we use kebab-case or another convention. #622
- [x] migrate the remaining HTML syntax to Markdown. #622
- [x] split the "model and cells" page which is too large. #622
- [x] adapt the content: remove ref to mxGraph code. #622