refactor: change the paremeter type to ITestFixtureFactory,

and delete DefaultTheoremAttribute(Func<ITestFixture>).
refactor: change the paremeter type of ConvertToTestCommand

Func<MethodInfo, ITestFixture> fixtureFactory
-> ITestFixtureFactory
refactor: change the paremeter type to ITestFixtureFactory,

and delete DefaultFirstClassTheoremAttribute(Func<ITestFixture>).
dev: implement and improve the FixtureType property,

of DefaultTheoremAttribute and DefaultFirstClassTheoremAttribute