git kill branchname

@charlierudolph Aaaaahhhh, for some reason some commits meant for this PR ended up in an already merged PR. I was messing around with `git extract` while being distracted on the resource planning call, so that's my (super lame) excuse... Anyways, please take a look at https://github.com/Originate/git-town/commit/738e3e76158a4803c5695abf71349b21d02033f5, and comment there. I will implement the corresponding fixes in this pull request, and once this gets merged its all going to be kind of okay again...  :smile: 
The method should do exactly what its name says it does. A method with name `commit_open_changes` should commit open changes. If it only does that if some global variable is set, then its name should be `commit_initial_open_changes` or something similar. But that strikes me as a strange method. I rather keep it simple and straightforward here, even if that means an extra line of code here. I think it is better readable: "given we have open changes, if we are killing the current branch, then commit the open changes, otherwise stash them".

Your version reads like "commit or stash", which makes the reader wonder why we do this always.