Refactor specs

This is a semi big refactor of the specs but it does the 3 following things.

1. Removes some unused helper methods and moves the fixture helpers from spec/spec_helper.rb to spec/support/fixture.rb
2. I refactored `construct_oauth_service` so that it would work for both windows and online services, then went through and removed all the duplicated OAuth and services setup from mostly the windows specs.
3. Lastly I moved the spec files so they mirror the file they cover. So now they are in `spec/lib/quickeebooks/`. I also moved and renamed some of the other files within there. This is the usual layout of spec files and makes it so things like guard-spec will work.

Other than refactoring to remove duplication the tests themselves haven't been changed. Let me know if you have any questions about any of it.