Extended HTTP DSL with "path" command and fixed "url" command.

Additionally, the `SendActionDefinition` has been refactored to avoid massive duplication
in subclasses.

What I remarked, too, is that `ActionDefinition` extends `Action`. This is IMHO not a wise decision since it results in a lot of "instanecof" calls which is a quite bad code smell. And yes, a ActionDefinition is **not** a Action (but a definition).

It would be much better to a have generic interface like `ActionHolder` with a method `getAction()`, implemented by `Action` and `ActionDefinition` and which is used in the test cases. `Action.getAction()` then can simply return `this`, while `ActionDefinition` returns the wrapped `Action`.

Just an idea ....