update bramble to 0.1.15, change default html and project level files

[cpirich]

• Update Bramble to 0.1.15, which includes these commits (context menu and default html changes):
  • code-dot-org/bramble@93e01ee
  • code-dot-org/bramble@d2362e0
  • code-dot-org/bramble@4fd6d5b
• Update the default html per design when you press the Add HTML button in Weblab
• Update the weblab project level starting files to match design (remove code.org logo, clean up index.html and style.css)

[islemaster]

Update seems great, but it looks like your generated yarn.lock does not line up with the one being generated in CI.

bundle exec rake circle:check_for_unexpected_apps_changes
rake aborted!
Unexpected change to apps/yarn.lock; if you changed package.json you should also have committed an updated yarn.lock file.

To fix, start with removing node_modules and running yarn locally again, and see if you get changes in yarn.lock. You may also want to double-check that you're using yarn 0.23.2 (the version we're currently locked to) as different versions can generate different lockfiles.

[islemaster]

LGTM if we can get Circle to pass 👍