OPAL-2647 Index property added to Variable, implemented for various datasources
OPAL-2655 Silently dispose datasources when removing them from datasource registry
OPAL-2612 Compute frequencies of continuous even though there are no intervals
OPAL-2656 Refresh hibernate table entities cache after transaction. Memory leak fixed in hibernate datasource
OPAL-2657 view set is synchronized
OPAL-2656 Entities refresh confuses the transaction
Code clean
Added some error logs when value table reference lookup fails