Refactor build

This refactors the spark build. The goals are to:
 * allow easy testing of the Dartium build, to know when our development target regresses
 * allow easy testing of the Chrome+dart2js build, to know when our deployment target regresses
 * build a version of the app w/o testing, so we're not shipping test UI to users

 * several grind tasks have been consolidated into `setup`
 * two new tasks, `deploy` and `deploy-test`. these do a polymer deploy, and then a dart2js compile. they also de-symlink directories. the output goes into `build/deploy-out` and `build/deploy-test-out`
 * the `archive` and `release` tasks are essentially unchanged.
 * all grind tasks are now public methods; all other methods in the builds script are private, to help separate out which is a build task and which a supporting method

I'l need follow on work on the tools/test_runner.dart script to be able to run tests against the Chrome+dart2js version.

@dinhviethoa @ussuri