grrrit: Allow filtering based on branches

Add posibillity to filter messages for delivery based on branch.

In the config, optionally a hash can be specified with a key "branch"
which contains a branch specific regexp.

For example:

    "#wikimedia-operations": {
        "operations.*": {
            branch: "^(?!betacluster)"
        }
    }

to filter out commits made to branch "betacluster" on all operations
commits.

Bug: 62232
Change-Id: I1f49d0d8363865b38a1b2d66f05cfecd930bc202
grrrit: Pass betacluster messages to QA

QA want betacluster branch commits to end up in QA channes and not in
main operations. Was specific only for apache-config repo, but made it
generic so all betacluster commits end up there

Bug: 62232
Change-Id: Icde91eb2c1f12f86b35b2b9670fce4836a90c419