Enable users of BuildCrossCheck to submit data without a token

[StanleyGoldman]

If a GitHub repository and it's associated build server project (on AppVeyor or others) is public, we should be able to:

1. verify the "in progress" build
2. determine what the associated GitHub owner repo is
3. accept the submission.

[StanleyGoldman]

I'm making the assumption that something the build process can write is something that BuildCrossCheck can validate against the respective APIs.

I believe codecov.io does this with their AppVeyor reporter. I believe it uses the name of the build in environment variables and validates that against the AppVeyor API.