Output inventories and ABOUT data as JSON

[pombredanne]

Beside the YAML and CSV formats, we should have support for a proper JSON output
Note that this would likely need to integrate ScanCode models first and then use ScanCode features for JSON.

[chinyeungli]

In the develop branch,
gen
We generate YAML format's ABOUT files from a CSV/JSON input
inventory
We generate an inventory in CSV/JSON format from the ABOUT files

so we already have support for JSON as an input and output