Conformance test for children/description/text props

[levithomason]

Some components will take a description or text prop. These props may also be defined using children.

In the case where children and another conflicting prop is defined, the children prop should win. We should be able to test if the current component is a Semantic component (see #70), and if it has a description/test prop, then test that the children prop wins if both are defined.

[levithomason]

Done and implemented.