fixed #84

The preparation and the execution of a PreparedStatement
happens now in a synchronized block.
The ResultSet can't belong the the PreparedStatement of
another Thread anymore.
Merge branch 'bug/84-submitInternalQuery-ThreadSafe' into dev
issue #85

This is just a workaround !
The bug can't happen anymore, if the method is synchronized,
but this makes the check for configAttr single threaded, which is
not very performance-friendly.
Merge branch 'bug/85-getConfigAttr-ResultSetAlreadyClosed' into dev