More notebook formatting and dynamic config

[jl-wynen]

Implements the ideas from the sjng branch.

• Dynamic config:
  • settings.json for application config
  • template directory with templates (.ipynb) and a config for each (.json)
• Include metadata in rendered notebooks, some in markdown cells, some in the notebook metadata. To see the latter, in Jupyter Lab, click on the gears on the right hand side and expand 'Advanced Tools'.

This is a first working draft of these features. We may want to change them when we get more templates to, e.g., share common schema fields between templates.