Added some tests for AXON-128
Forgot a file in previous commit
Improved documentation on @CommandHandler parameters

The documentation did not mention the ability to use ParameterResolvers that
allow e.g. Spring beans to be passed as parameters.

Issue #AXON-127 Fixed
SagaTestFixture will now do shallow field comparison on Commands

Commands do not always implement an equals method. Yet, the fixture should
not really be influenced by that. Now, when a fixture compares commands, it
will first check for equality using equals. If that is false, the fields are
checked using their equals method.

Issue #AXON-111 Fixed
Tests seemed to influencing eachother