Add environment variables for the writable file paths

[zepich]

Idea

Changing the paths where mosparo stores the generated files (for example, the prepared CSS files for the frontend) can be interesting for different use cases. In a multi-node setup, for example, it can be interesting to store the files in a different, synchronized location but without synchronizing the whole mosparo code.

For this, we add three (or more) different environment variables with which it is possible to define an alternative location to load and store the configuration file, the CSS files for the frontend, the data directory to store the GeoIP2 database, import files, and more.

Inspired by

• @raul810y

Discussion

• Install mosparo with high availability #285