->newMockedInstance

This PR add the `newMockedTestedInstance`/`newMockedInstance` property handlers to `atoum\test` class as discussed in https://github.com/atoum/atoum/pull/320

The `mockTestedClass`already exists but it does not really achieve the same goal : it instantiates and returns a new mock instance of the tested class.

What `newMockedTestedInstance` provides the same functionality in a different manner : it instantiates a new mock instance of the tested class and wires it to the `testedInstance` property (which has been introduces in this PR)