Allow parameters to be specified as meta properties

As suggested by Paul, parameters may be specified as Meta properties:

Meta: 

@theme parameters

Scenario: 

Meta:

@variant named

Given I have specified the <theme>
And a <variant>
Then the theme is parameters with variant named

The named meta parameters would be matched by usual @Named mechanism, also used in story or scenario parametrisation.

@Given("I have specified the <theme>")
public void givenIHaveSpecifiedTheTheme(@Named("theme") String theme){
    this.theme = theme;
}