add django app for deployment and update to latest version of dasf-web

This MR updates the fee-river-plume-workflow to the latest version of dasf-web (0.3.4) and it introduces a django package for deployment. When you call npm run build, the static files are built directly into the python package (located at python/fee_riverplume_workflow) and are shipped to the deployment when you build a python package (e.g. via python setup.py sdist).

You can use the local django project in testproject to start the development server. There is no pulsar needed anymore. The installation instructions for python are described in the README.

@viktoria-wichert it would be great if you could test the installation locally before I set it up at https://hcdc.hereon.de/datahub. Please let me know if you want to do it together. Everything should be described in the README of this branch under the section building the frontend and Deployment (locally).

to run this frontend, you need a backend module that is compatible with demessaging 0.3.0 (see digital-earth/de-synopsis-backend-module!29 (merged))