Allow using the http driver with dlite.storage_path

[jesper-friis]

Goal: allow to use online repository of data models in dlite.storage_path (e.g. stored in a public git repository).

It should support different backend drivers, like json, yaml, ...

This could be implemented as an improved version of the http driver.

GitHub driver
To support query on data models stored in a github repo, one can use the trees API. For example: https://api.github.com/repos/HEU-MatCHMaker/DataDocumentation/git/trees/master

Should use subdirectory URLs, like https://api.github.com/repos/HEU-MatCHMaker/DataDocumentation/git/trees/46d909ade1423ceb17f5a3933ad12bb724d5d0fd

Subdirectories can be reached by recursively following the url links. Alternatively, add option ?recursive=1, as in https://api.github.com/repos/HEU-MatCHMaker/DataDocumentation/git/trees/master?recursive=1. Some help functions for finding the subdirectory URLs can be provided.

Probably better to implement this as a dedicated github storage plugin.