[Delivers #41508431] surface the record's level in the tree

Adds an optional 'level' to the record_tree schema and is populated for any record that has a 'level'  (NB digital object components do not).

This value is translated in the frontend before being rendered (as it is an enumeration).

PR also contains a patch to fix pagination for frontend search results - they would always return page 1 of the results! (symbol vs string test failcake).