Removed 'setSticky()', 'nodeExists()' methods from DbConnector + updated...

Removed 'setSticky()', 'nodeExists()' methods from DbConnector + updated 'insertNode()' + decreased num of connections to db for each class, added 'storageType' param to DataRpcServer + added basic handling for TimeoutError exception in Mailer class + code cleanup.

Signed-off-by: Cristiano Urban <cristiano.urban@inaf.it>