create branch per stage and push it to repo after each deploy

[adamszeptycki]

After deploying it will create a new branch (or check out existing one) with the same name as stage and push it to remote.

[revmischa]

maybe a makefile target would be more readable. could have each command in a separate line and it'll tell you what failed and could have dependency in it, like check for dirty working tree

the sls script could call makefile