Heading Test

[cypherean]

To be merged after #541 and jywarren/woofmark#5. Tests adding a heading and switching b/w different heading sizes.
Make sure these boxes are checked before your pull request (PR) is ready to be reviewed and merged. Thanks!

• tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR -- or run tests locally with grunt jasmine
• code is in uniquely-named feature branch and has no merge conflicts
• PR is descriptively titled
• PR body includes fixes #0000-style reference to original issue #
• ask @publiclab/reviewers for help, in a comment below

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Thanks!