Less memory footprint by facet navigation URLs

Facet navigation URLs need much more memory for internal processing then regular URLs, because there's a new JCR session involved per URL (if I understand correctly).

This makes a site implementation susceptible to going out of memory if many of those URLs are requested at the same time, for instance when a site is crawled by bots.

In a concrete case, an out-of-memory occurred in a project and the heap dump showed 56 HippoLocalItemStateManager objects, which correspond to JCR sessions.

The biggest one retained 115 MB, from a 4-level fac nav URL with a pretty standard implementation behind it, using org.hippoecm.hst.util.ContentBeanUtils#getFacetNavigationBean().

The second biggest one retained 47 MB, also from a 4-level fac nav URL.
Then 43 MB, 41 MB, 31 MB, all from fac nav URLs.