And fix the zillion issues that uncovered.

This reverts commit f41b3411, reversing
changes made to e33d8d96.

This was a bad check-in due to my mangling uploading a new version of the branch from a different machine.

This reverts https://github.com/flutter/flutter/pull/2639 and will be replaced by https://github.com/flutter/flutter/pull/2640

And fix the zillion issues that uncovered.

Previously we used a positional argument for widgets that had multiple
children. Now we use a named argument that defaults to an empty list.

Fixes #241

Also, clean up the main.dart file to prepare for making dynamic theme changes.