SQLFeatureStore: SELECT improvement and streaming fix for multiple-featuretype queries (BLOB mode) 

Adds the following improvements for BLOB-mode queries that target multiple feature types:

* Better SELECT strategy that uses UNIONs and an ORDER BY based on constants instead of the crude string function used before
* Add missing calls to Statement.setFetchSize (...) to enable streaming result sets

3.4 version: https://github.com/deegree/deegree3/pull/318