Refactored the REST resource type folder.

Hopefully the flow of HTTP requests is clearer now.

Also changed the handling of GET request for the actual resource folder.
It now returns a list with the indexed values of all resources in the
folder. The old behaviour was to return a list with all registered
indexes and resources. This is now available by requesting the ".meta"
resource of any resource folder. I also had to change some tests so they
use the ".meta" resource.
Adding limit and offset parameters to folder list.
Filtering for the resource folder.
Small bugfix in the error handling.
Fixing component browser.

It now adheres to the /.meta resource.