EZP-23089: REST siteaccess API

> Status: RFC
> Issue: http://jira.ez.no/browse/EZP-23089

Simple approach: a unique resource lists siteaccess the user can login to.
IMO, we should use plurals for the requests. I mean instead of **site/siteaccess** we should use **site/siteaccesses**. It is easier to provide limits then. What do you think?