[DEVEXP 391] Add source info to build, buildConfig and eval a new build ...

@bparees @ironcladlou @pmorie @csrwng Please review
We need to validate that the commit belongs to the branch we're interested in. The github event includes the ref that the push was for: https://developer.github.com/v3/activity/events/types/#pushevent. We should compare that with the ref we've been given in the source input (and if no ref specified, that the commit corresponds to master).