[added] <DefaultRoute> component

Also, changed behavior of routes with no name, path, or children so
they act as default routes. <DefaultRoute> is essentially just sugar.

Fixes #164
Fixes #193
we need @spicyj to show us how to do this properly before the next release of react, apparently we are cheating here and need to make components, not just functions that can trick JSX, but for now :shipit: