Clean up layouts, add documentation

@bentedder Looks like a lot of files have changed, they've actually just been moved. Git is confused.

What it actually does:
- Removes global_resources_controller. Legacy routes are now pushed through layout_controller.
- Moves /custom_layouts to /layouts/custom
- Renames /layouts/core to /layouts/partials
- Moves /global-nav to /layouts/examples
- Adds some documentation
- Routes /layouts to the documentation - with a list of the layouts