isStatelessComponent: Handle Logical and Conditional Expressions

[danez]

Besides refactoring the module it now supports components that return
LogicalExpressions or ConditionalExpressions. I also removed the "manual" scope check
and instead use the scope returned by ast-types and compare that one.
The test have been rewritten to be composed of certain parameters instead
of hardcoding all possible testcases.

function MyComponent () {
  return a ? <jsx /> : b 
  // or
  return a || <jsx />;
}

This should improve some cases reported in #232

A further improvement would be to also account for .forEach, .reduce etc.