Split mapper into various files for better organization

As part of GSOC 2014 we're refactoring the routing mapper.
This is one of the many PRs we'll open to integrate into Rails over the next 2.5 months
This needs to be refactored to look like our final organization
\cc @pixeltrix 
I know I haven't yet firgured out how to implement resources. The hash model system is difficult to convert to a pure OOP one. Will have to think more about it but do you like the concept of running dsl helpers as instance methods of the current scope?