Datacage: Add a pool of builders to make it multi threadable. XML DOM is not thread safe. Therefore the old implementation only allowed one thread to use the builder at a time. As the complexity of the configuration has increased over time this has become a bottleneck of the whole application because it took quiet some time to build a result. Furthermore the builder code path is visited very frequent. So many concurrent requests were piled up resulting in long waits for the users. To mitigate this problem a round robin pool of builders is used now. Each of the pooled builders has an independent copy of the XML template and can be run in parallel. The number of builders is determined by the system property 'flys.datacage.pool.size'. It defaults to 4.

next.gauge.id = \
    SELECT GAUGES_ID_SEQ.NEXTVAL AS gauge_id FROM DUAL
next.timeinterval.id = \
    SELECT TIME_INTERVALS_ID_SEQ.NEXTVAL AS time_interval_id FROM DUAL
next.discharge.id = \
    SELECT DISCHARGE_TABLES_ID_SEQ.NEXTVAL AS discharge_table_id FROM DUAL
next.discharge.table.values.id = \
    SELECT DISCHARGE_TABLE_VALUES_ID_SEQ.NEXTVAL AS discharge_table_values_id FROM DUAL