Rework discovered license to support the Go ecosystem

[fossygirl]

In the Go ecosystem the licenses will be discovered and declared in slightly different places from what we're used to in other ecosystems. To support this, we will want to map subpackages to the same source location as the parent. If a license is detected at www.bar.com/go/**foo**, that would still be included in the discovered licenses, but wouldn't be interpreted as the declared license. We would still treat the top-level LICENSE file as the declared license for all go packages that are in the git repo.

@rspier @jeffmcaffer for visibility

[fossygirl]

Closing.