(waitForReadyConnected, waitForAuthenticated, waitForMailSent)
synchronous waiting.
Added writeToDevice() function to MimeMessage and MimePart (and
subclasses), now these are used in SmtpClient instead of toString().
Added some unit tests.
- fixed the bug related to ELHO message: "ELHO SmtpClient for Qt/C++"
changed to "ELHO " + name, the name is now by default "localhost"
- added setter and getter for the name used in the ELHO message
- added virtual attribute to prepare() method in all classes
- added virtual attribute to toString() in the MimeMessage and
MimePart classes