VCIO-next: Create improver to find fix commits

[pombredanne]

We should collect fix commits from existing references using a new improver.

This improver pipeline that will scout the References to create CodeFix entries.

This will be using the CodeFix models designed in:

• VCIO-next: Add support to track fix commits: Include commits and patches that fix a vulnerability #207 (comment)

And is in support of the larger fix commit collection issue at:

• Collect all fix commits #1703

See also these related issues:

• Infer Package URL from references and other references issues for "commitish" URLs  #327