Introduce new CONFIG changes blocker for commit_compare webhook

This MR proposes the feature described by #183. There is a major difference between the script that is being executed by Prarit and this webhook. The script clearly checks for all opened MRs and their changes to inspect CONFIG mismatches. If some inconsistency is captured, the script blocks the MR. It als includes some optimizations to check the differences because Python is smarter than shellscript for some kind of parsing.

IMHO, for webhooks, the idea is even simpler. We could inspect just new MRs and their dependencies. And, as I think it is not so complicated, it could be part of commit_compare webhook instead of a stand-alone webhooks. We could use all the facilities provided by that webhook to check configs accross streams.

Signed-off-by: Julio Faracco jfaracco@redhat.com