Feature/first run feedback

Incorporate feedback for the "first run" page from the mailing list. There may be a few additional changes I'd like to make before merging, such as

1. Do version detection in JS and only maintain one "first run" page, since the difference between the pre-Australis and Australis pages is so minor.
2. Try to have a link that opens the Lightbeam tab in the "first run" page. Might be possible with `window.postMessage`.