Provide project wide default branch permissions

In order to reduce the maintenance effort of configuring branch permissions across multiple repositories
As a Stash Administrator
I want to be able to set default branch permissions for all repositories within a Stash project, unless explicitly overridden in the repository

Background

Currently it is necessary to configure branch permissions at a repository level. We have hundreds of repositories, split between a few dozen Stash projects. It would make life much easier if we could define our branch permissions at the Stash project level, rather than on the individual repositories. Our permissions are typically the same for most of the repositories.