Add support for License Policy

[steven-esser]

In relation to aboutcode-org/scancode-toolkit#880 and aboutcode-org/scancode-toolkit#214

This could probably use discussion, but once a license policy plugin is implemented in scancode we would at least need some visual indication of a license that violates some given license policy.

These can be handled as icons.

[DennisClark]

Here is a basic description of the license policy flow:

• Create a license_policy conifguration file.
• Reference the license_policy configuration file when running a scan with scancode-toolkit, specifying the option to include license-policy in the output (license, label, icon, color_code).
• Display the license-policy data in the details presented in the AboutCode Manager tables.

Enhanced data flow to be described later.

[steven-esser]

Will address this in the next minor version ABCM release, as it will require schema changes to implement. #309 and #310 lay the foundation for how files/packages with policy violations will be displayed to the user.