Allow Regex in uri_params configuration

Currently, to cache categories with layered navigation properly, all filterable attributes have to be added to ``uri_params``.
It would be nice to allow regular expressions in this configuration, so that for example you can prefix all codes of filterable attributes with "filter" and add ``/^filter/`` to the ``uri_params``

To keep backwards compatibility, I implemented it so that entries in the configuration enclosed by ``/`` are treated as regular expressions, all other as normal strings like before.