Provide support classes for inserting authentication information in logon messages

What do you think of modifying the logic for sending Logon messages to optionally include the username/password?

While it's possible use QFJ to construct our own Logon message and send it out in the application logic, it's rather non-trivial to do so.

I propose to add 2 new parameters to SessionSettings (username/password) that, if exist (and if DataDictionary has these fields for the given FIX version) would include the username/password in the logon message.

See the attached patch. I couldn't figure out how to create the acceptance tests for it. I also realize that we may want to add extra logic to make sure debug messages don't print the password fields, and maybe a better way to encrypt/obfuscate the password.