MIRTH-1066: Added the ability for subclasses of FtpConnection to issue custom commands after a connection has been established.
The default data pruner block size is now set to 50000
Issue: MIRTH-3474
MIRTH-3432

Fixed the message sequence migration so that it only performs the migration if the D_MESSAGE_SEQUENCES table exists. If the user is migrating from version 2.x or if no channels had been previously deployed, then this table would not exist and the migration would throw an exception without this added check.