Show player one bold to start

Use a new property on the user, `isTheirTurn`. This will
be used throughout the app to indicate various hints of the
player turn status.

See #14
Merge branch 'master' into indicate-turns
Implement the idea of the local user

The local user is marked as such when the code for adding a student is
run. In the future, this will most likely use the OAuth access token to
identify the current user.

This commit will block the input box if it is not the students turn to
write.

See #14

See empirical-org/Compass#269
Take turns writing

Now, using a firebase reference on each student combined with ng-disable
and knowing the "local" student, we are are able to properly take turns
writing the story.

See #14
Merge branch 'indicate-turns'