Adding sample hop runner

This should "just work" by running `pub update && dart tool/hop_runner.dart pages`. The runner will build all samples with dart2js and dart2dart then deploy to the `gh-pages` branch on github. The index page is generated from the `tool/hop_runner.dart` script. An example deployment can be seen http://financecoding.github.io/dart-tutorials-samples/

When hop lands some additional changes this script will become much smaller without all the extra methods.