Allow repo names with ".git" in them

@charlierudolph @allewun   implements #305 

* fixes a bug where repo names that contain ".git" are improperly handled when creating PRs. This happens if you want to create a PR for an Originate blog post. The repo name there is "originate.github.com".

* simplifies the repo specs. The repo specs always seemed over-engineered and cryptic to me. What does "HTTPS not ending with .git" mean? How exactly does the respective URL look like? Does this really cover all possible remote URLs? This over-optimization made the specs hard to read, and hard to maintain.

  I needed to add a different repo name to the specs, and that made the existing tables completely ridiculous. So I simplified them. Now we can give as many different origin URL as we want, even broken or strange ones, and make sure Git Town behaves correctly. The spec becomes more understandable for strangers, and I was able to remove a good amount of pretty complex test infrastructure.

What do you think?
Well, technically it belongs into pull_request_steps. 

`@last_run_result` is a global variable, I'm fine with using it in multiple files. I'd say that following the proper file naming strategy weights heavier than only using a global variable in one file. What do you think?