Property: delete old unit test
Property more tests.

- add Property::operator<<()
- add Property::opertator=(nullptr_t)
Property: adapt setter and getter to naming schema

- Property::getValues() -> Property::values()
- Property::setValues(...) -> Property::values(...)
Merge pull request #63 from stoewer/master

Property: tests and minor refactoring

Also part of unit-test meta issue #25
Looks good to me.