Bugfix/ckg internal server error

[nilskre]

Hello, Current state:
When checking out the CKG project from the master branch and running the CKG App it returns "500 Internal Server Error". Cause of the error:
This error is caused by the interaction of a new Jinja dependency (the version is not fixed in the requirements.txt) with old flask/dash dependencies. As described in this Issue Flask(1.0.x) and Jinja2(3.1.1) are not compatible.
Related CKG issues:

• Issue 83
• Issue 87
• Issue 85

Implemented bugfix in this pull request:

• update dash and flask from 1.x.x -> 2.x.x (ensures compatibility with newer Jinja2 versions)
• simplify dash multi page code by using the new multi page app support
• set all dependencies in requirements.txt

Thanks in advance!