RFC: Report all detected license data by expression

[pombredanne]

Today we have a combo of reporting by license key and by license expression.
Since we detected license expressions, we should always report everything by license expression.
This would mean a significant output data structure change:

• The licenses file attribute would go away.
• Instead the detection details would be provided under the license_expressions
• We should avoid to repeat each license details and instead introduce a top-level licenses codebase attribute that would list the detected license reference information (and could optionally include the standard license text)

[AyanSinhaMahapatra]

This is merged and in develop now. We have license references reported seperately and license data is reported by license-expression and not license keys.