Bug 253354

We should have a pre-push hook that makes it difficult for contributors to push content we know contains security sensative changes. We have 3 ways of knowing this: 1) The commit a user is trying to push already exists on a different remote with a higher secuirty level than the target remote 2) The commit a user is pushing is a cherry-pick of a commit that already exists on a different remote with a higher security level than the target remote 3) The commit being pushed references a security issue. In most circumstances, we should outright block the first case and prompt the user for cases 2 and 3. The 'git-webkit publish' workflow should prompt the user in the first case, but block cases 2 and 3.