Extension methods against ScreenFixture

[jmarnold]

Putting this here before I forget:

Much like we have the "EditableElementsForAllImmediateProperties()" in the ScreenFixture, I'm thinking that we enable a mechanism to do the same modifications through extension methods.

Example:

[FormatAs("There are no validation messages")]
public bool NoMessages()
{
    return !validation.AllMessages().Any();
}

[FormatAs("The validation summary is not shown")]
public bool NoSummary()
{
    return validation.Hidden;
}

public IGrammar VerifyValidationMessages()
{
    return VerifySetOf(() => validation.AllMessages())
        .Titled("Verify the validation messages")
        .MatchOn(x => x.Property, x => x.Message);
}

That's WAY too common to write in every fixture. It'd be nice to be able to inject the grammars via an extension method you can call in the fixture ctor. Maybe?