We can build Fitness again now that playfair has been updated to account for
the package:flutter rename.

Also, introduce Colors and Typography to hold the material colors and the
typography declarations. Previously we expected clients of these libraries to
import them into a namespace, but that doesn't play nice with re-exporting them
from material.dart.

We need the new version because of the TextPainter rename.

@collinjackson

... and reattach fitness to the build. We detached fitness from the build
because it was seeing an old version of playfair that didn't work with the most
recent version of the Sky package.

Now it wont crash on save, but it still doesn't display
the error message in a snackbar and this also doesn't
wire up the enter/go key to actually do anything.

We'll need to implement performEditorAction on our
InputConnection implementation to catch this key and
pass it along to dart.

Our Input control needs to get more powerful to handle things
like this, including filtering of input.

The code was crashing by triggering a bug in the SnackBar
which didn't assert for actions, but crashed when they
were not null.

Partial fix for https://github.com/domokit/sky_engine/issues/543

@abarth

This required me wrapping the new Activity APIs
as well as adding the missing pubspec.yaml

@abarth