Enable running only single test class or method

To configure, set values for `project.spoon.className` and `project.spoon.methodName`.

To enable setting class/method from command line, project may be configured like this:

```groovy
spoon {
    if (project.hasProperty('spoonClassName')) {
        className = project.spoonClassName

        if (project.hasProperty('spoonMethodName')) {
            methodName = project.spoonMethodName
        }
    }
}
```

`gradle spoonMyProjectTest -PspoonClassName=com.myproject.test.SomeTest -PspoonMethodName=testHomeScreen`

However, project property names are completely arbitrary. Yu may also use Java `System.properties`, e.g. `-Dspoon.methodName=...`