feature: git phlow wait

[groenborg]

As a developer using the phlow workflow and I need my changes integrated into master before I continue I want git phlow to wait and notify me when changes are available and have been integrated by the CI service

git phlow wait Is a blocking operation that waits for your feature SHA or any given sha to appear on master, and will notify you when that happens, this way you do not have to monitor your CI service manually to know when you can work on something new.

We have identified three separate scenarios where it should behave as following:

• If I am on a delivered feature branch, --wait will watch specifically for my changes to arrive back on master, then exit. Then I would be ready for the next workon.
• If I am on master, --wait will wait for any incoming change. This would be useful for instance when waiting for a push from a co-worker of changes that you need before starting new work.
• If I am on a non-delivered feature branch, it should wait for incoming changes on the tracking branch (integration branch), and exit when there is something new. Then I can choose to do a git pull --rebase myself of I want the changes.