Create a "collect_manifest" scan option to generate a lockfile when none exists

[DennisClark]

Proposed: a new "collect_manifest" scan option that prompts scancode to figure out the dependencies when there is no clearly specified manifest, and then store that generated lockfile in the scan results.

Benefits:

• Better dependency results
• Traceability of the dependency results by making the generated manifest persistent

[pombredanne]

After consideration, we would rather not have a scancode option for this. Instead it will be a separate standalone executable that is tracked in https://github.com/nexB/dependency-inspector/ and specifically in this issue:

• Create a Lockfile checker and generator  dependency-inspector#2