Add ability to limit build triggers to specific branches

We have a build pipeline that needs to work something like this:

1. commits to a repo trigger unit tests / war packaging for all branches (bamboo auto-manages branches)
2. IF the commit was to our production release branch, then we need to trigger multiple other builds which will generate machine images that can potentially be deployed (after going through a manual QA process)

Currently, the only options for build triggers are (a) repository polling, or (b) scheduled. Repository polling would work, but we need to restrict it to only firing off the dependent build if the commit activity was on a specific branch.

This is roughly analogous to how deployments can be restricted to a specific branch. However, deployments don't work for us in this case as we need to trigger multiple processes.