Improved version of Rhino environment. Intergrates better with sbt for `test` and `run` tasks.


- Tests can now be run using the built sbt in test facilities. To use it you need to add a dependency on a Scala.js test framework (for example Scala.js jasmine test framework) and add a marker interface (`scala.scalajs.test.Test`) to your test classes (or extend JasmineTest when using the Scala.js jasmine test framework).
- The default Scala.js test framework and Scala.js test bridge class can be changed using sbt settings
- Provided a reference implementation of the test framework using jasmine
- Added experimental support for `env.js` in the run and test environement. Just add `env.js` webjar as a dependency your project.
- Run command now searches for objects that have a `main` method (normal sbt behaviour)
- Added example to demonstrate testing with jquery and env.js.