Remove pow

Pow seemed like a great idea to access different development sites with nice URLs like `base.dev` or `bla.dev`. But it suffered a possibility to use it with Pry in the way that I like: both output of the server and pry sessions within the same terminal!

So I switched back to webrick. This offers exactly what I need. I also implemented a way to set the default port per application, so we can run different development sites beneath each other without having to specify different ports manually.

The only drawback so far is that I didn't find a way to restart webrick automatically. I managed to stop it using guard-shell, but restarting has to be done manually at the moment. More infos here: http://stackoverflow.com/questions/22465596