Fix (implement?) deep linking to a justification

[carlgieringer]

The app currently has a Justification context menu item "Link" that adds a fragment like #justification-1921 to the URL. I remember the intention was to share this URL and that Howdju would scroll the page to put that Justification in view. This would be useful on a Justification's page having a lot of justifications, for example. In the future when we might not load all of the Justifications, the app should also be sure to request this justification specifically from the API.