Improve ScanCode packaging and reduce wheel size

[AyanSinhaMahapatra]

It would be nice to package the license data and the built license index as separate wheels to reduce the total wheel size, as we are hitting pypi wheel and project size limits.

Reference:

• Project Limit Request: scancode-toolkit - 20 GB pypi/support#3027
• Release scripts failing #3435

The flot tool has been designed to help with this: https://github.com/nexB/flot

Some todos:

• Create separate wheel(s) for the license data and license index
• Refactor how SCTK is built to use separate license wheels