Removes constants file from GoodLooking

This rather misguided file defined some "enums". It hasn't been in use
ever since the poor error handling was removed in f6f2417 but it hadn't
been removed yet, so this commit does that.
Adds autoloader

Adds a psr-0 compliant autoloader to the project. I am thinking about some
changes to it still (like making sure it only loads \Good\ classes - even
though that shouldn't be necessary per see), but we do have a working
autoloader now.
Introduces the usage of the autoloader.

(That basically just means it removes include and require statements
everywhere.)

This closes #6