Refactor LocaleSelect to work with valueLink

This makes the LocaleSelect React component work in situations where
the React ValueLink add-on is used.
Rename Code component to CodeBlock
Add more React propTypes validation
Improve rendering of examples using tab view

This adds a tabbed interface to the various source code snippets that
go into making up an example. Overall these visual changes make it
easier to view an example's source and output as a whole unit.
Merge pull request #81 from ericf/example-rendering

Improve rendering of examples and composition of React components