Refactoring

I had some problems using the template properly, so I made some changes:

• fixed the reveal.js to a release version (git submodule) and the node version (.gitlab-ci.yml)
• refactored the presentation.html, now it can be opened directly in the browser (requires a build of the GFZ template)
• removed the run_local.sh and replaced it with:
  • build-gfz-theme.sh, builds the GFZ theme. After building the presentation.html can be opened directly
  • run-server.sh, runs a live server as described in the reveal.js manual. This generates the reveal.js/index.html from the presentation.html
• updated the README.md

Scripts for Windows users would be great. Also don't know if the scripts work for Mac OS.