Enable searching in additional class paths for webjars.

* Some webjars may not be packaged in org.webjars package.  This change enables searching additional packages.
* Add some unit tests, including a sample webjar and a sample custom-packaged webjar.
* Added a Builder for instantiating WebJarResource.
Manage bootstrap with maven.
Merge pull request #4 from joeslice/more-loaders

Enable searching in additional class paths for webjars.