Organize sky/framework a bit

- Removed out-of-date README.md
- Moved fling-curve into the animation directory because it's part of the
  animation behavior of the system.
- Moved view-configuration into the theme directory because it's a collection
  of constants similar in flavor to the colors and the shadows. Eventually
  we'll want to make the theme configurable and have these all together will
  hopefully make that easier.
- Moved dom-serializer into tests/resources because it is used only by tests.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/980423002

examples/fn/widgets/widgets.dart

 library widgets;
 
 import '../lib/fn.dart';
-import '../../../framework/fling-curve.dart';
 import '../../../framework/animation/curves.dart';
+import '../../../framework/animation/fling-curve.dart';
 import '../../../framework/theme/colors.dart';
 import '../../../framework/theme/shadows.dart';
 import 'dart:collection';