Django-geo-spaas

bug fix of viewer styles (css file)

- add an extra template to the base viewer to display dataset information based on various viewers
- base viewer highlights the polygon when hovering over the result table
- datasets without geographic location are excluded from the search results

The base viewer can hide the local file location of downloaded datasets

Removed the length limit on the `Dataset.entry_id` attribute.

- Updates to the README file
- A slim image based on nansencenter/nansat:latest-slim is now built
- :warning: **The intermediate `DatasetParameter` model has been removed**
- the new migration needs to be applied on existing databases
- when applying this migration, existing relationships between datasets and parameters will be lost