Devoncarew spark startup

This allows us to run spark in dartium w/o having to first deploy the code. It works around an issue with the latest polymer not working in a CSP context (when not deployed). Essentially, the `spark_bootstrap.dart` in-lines the things that would otherwise be done dynamically (requiring script generation); it returns w/o doing anything if run in the deployed context.

I am seeing frequent timing issues at start up; hopefully resolved w/ some of Sergey's refactorings.

@dinhviethoa @ussuri @jmesserly