Mara-page

- Add parameter `div_id` to functoin `asynchronous_content` + minor changes

- implement hashing of navigation entries

- page rendering experience improvement: function `html.asynchronous_content` now sets the height of the placeholder diff to the previous height from local storage

- many refactorings
- delayed rendering of html in `response.Response`
- performance improvements in `xml` module
- improved html markup in `bootstrap.card` and `bootstrap.table`
- new function `bootstrap.button`
- custom "permission denied messages" in `acl.require_permission`
- new function `html.asynchronous_content` for loading parts of a page throug ajax
- new function `html.highlight_syntax' based on pygments

**required changes**

- `bootstrap.card` has a new signature, please adapt calls

- Added functions for creating boostrap cards and tables
- Navigation entries can be hidden by setting `.visible = False`

- Added function `user_has_permission` to acl interface