Changes to Pathauto

I've reviewed the current state of the pathauto module. 
As I'm new to D8 development, I did some minor changes I saw during the reading of the code.
Don't worry about it for now. We're working on making the different pathauto pattern types plugins in https://github.com/md-systems/pathauto/pull/15, so we can possibly easily add a method somewhere in here or even move most of the logic here into a default method of a plugin base class.