[#1337] Removed server_class and configuration_class attributes. Updated version...

Problem description
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The following attributes are no longer used, they need to be removed:
 * `server_class`
 * `configuration_class`

Changes description
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I've removed the attributes and fixed the typos in the docstrings.

How to try and test the changes
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reviewers @adiroiban 

Please review the code changes. Make sure that all the tests pass.