Add Go.CD build history API call

[RehanSaeed]

Raising an issue as per contributing guidelines. This method added to the Go.CD build provider calls the Go.CD API to get build history information about the current pipeline (build). This can be used to get information about what triggered the build and also the git changesets that triggered the build. This is really useful for adding release notes.

[gep13]

@RehanSaeed I have just merged this in, thanks for your contribution!