Support "git flow" branches, optionally create PRs

[cball]

When using git flow, the branches are setup in the following way:

• dev (alpha)
• beta (beta)
• release (master)

In this mode, the script currently tries to delete the local copy of master, which is not good.

This also brings up concern of protected branches. I see 3 scenarios:

• ci does the commit, and ci is a protected user that is allowed to push to master & dev
• push to an intermediate branch, open up browser to create a PR
• require protected branches to be off

My concern with the PR flow is that if the PR is not immediately merged, the history will be wrong.

[cball]

We should recommend a machine user and allow that user to push to protected branches. As a fallback, we can suggest removing branch protection. I think the PR workflow is just asking for trouble