Four functionality additions to make roots-contentful more flexible

[davidgustys]

1. Added ability to namespace
   Now you can specify were "content_type's" are attached globally and per content_type, rather than always getting assign to "contentful".
2. Content_type now has 'set_locals' function
   Basically ability to set "content_type" locals manually rather than always automatically
3. Path function now has second parameter passed containing all content types(deep cloned)
   Very useful when you need 'data' form other content_type for curren type's path generation.., i.e having meta content_type, on which other content_type may depend..
4. Minor execution flow reordering
   Basically set "urls"/ write files right before compilation, so that path fn, has all the data for really custom path generation..

[zspecza]

Hi @gdeividas! First off, thank you very much for these wonderful additions to roots-contentful. They'll be very useful and the inclusion of tests is 🅰️+

Secondly, I would like to apologize for not responding to this PR sooner. I've been having a few issues with notifications on Github, so it didn't quite catch my eye until now as I have focused my attention entirely on development.

However, roots-contentful is undergoing a major refactor to ES2016 at the moment.

Is there any chance you could open a separate PR that adds these features to the es2016 branch? I can merge them in there and then they will be included in the next release.

Be sure to read the updated contributor guidelines for that branch for any information on development processes