Implement a ScanCode detection diff report for ScanDatabase

[fviernau]

given:

• Two ScanCode versions
• database with scan results
• package configurations / curations

output a table with rows per package showing:

• diff in offending licenses and
• diff in the packages clearance state

scope:

• limited to packages / dependencies

use cases:

1. Understand the impact of switching between two ScanCode versions on the scan results / rule violations
2. Identify which preparations to make when migrating between the given ScanCode versions, e.g. fix scan issues beforehand, classify upcoming new / unclassified licenses
3. Decide whether the old detection capabilities are still good enough to keep on using or not, e.g. if the lack of an important detection capability gets discovered / known that may lead to the requirement of not using that old version anymore.

[fviernau]

Not planning to work on this anytime soon.