Add classification tests

[ipoerner]

The whole classification engine has only been tested with external tools thus far, so as soon as issue #9 has been resolved, a new group of functional tests should be incorporated into the test suite, targeting the successful classification of selected IMAP servers.

[ipoerner]

I seem to have created a circular dependency in the issue list :-) Anyway, the classification tests may also be done prior to solving issue #2.