MOBSDK-542

Allow users do set custom CMIS binding via session parameters. This can be passed into the AlfrescoSession as part of the parameter NSDictionary. A new constant has been defined for that purpose in AlfrescoConstants.

A new test has been added in AlfrescoSessionTest to verify that indeed the custom binding is used.

I noticed there is a bit of redundancy in the test base class that could do with some cleaning up.