License data structure: In ouput include SPDX expressions, report matched rule by expression and do not report individual licenses

[pombredanne]

In ScanCode output include SPDX expressions, report matched rule by expression and do not report individual licenses. Licenses should be reported as their own top-level "licenses"

[AyanSinhaMahapatra]

This is completed and merged.

detected licenses are reported by license-expression and no license keys, and license reference data at top level.