Admin rights check

[joepio]

Spec discussion: atomicdata-dev/atomic-data-docs#82

When processing search or collection queries, by far the most time is spent on iterating over every resource, and recursively checking whether the user has the correct rights.

A very simple way of speeding this up, is to check if the user has some root level / admin level rights. That way, we could skip all these checks, and make things way faster.

Relates to #279

[joepio]

Perhaps when implementing this, I should also update the default .save behavior, since that one uses the default_agent, which should probably have admin rights if we fix this issue.