Add package_releases in packagedata model

[TG1999]

Signed-off-by: Tushar Goel [email protected]

Add package_releases in packagedata model to have more than one downloadable url per package

[TG1999]

@AyanSinhaMahapatra @pombredanne @JonoYang please have a look on these model changes, please give your suggestion on this and do let me know if these model changes are useful in anyway. We can remove all the fields from the PackageData model that will be shifted to PackageRelease after we migrate these fields to PackageRelease model.

[pombredanne]

@TG1999 IMHO we should close this and instead have an issue to revisit the topic of packages vs. download URLs.

[TG1999]

Added issue https://github.com/nexB/scancode-toolkit/issues/3188