add EasyRdf as submodule

it provides a good Rdf export, so we do not need
to develop our own solution
remove further zenddb/mysql leftovers; implement general rdf-export

Support general rdf export using EasyRdf. It does not
matter if the current adapter supports it, the store
class does.

wrote test for rdf-export for all supported formats.

Get rid of further zenddb/mysql stuff in the tests;
remove according code or files.
use latest zend framework 1.x release (1.12.3)