Make result of sharing action clearer

[parente]

When a user clicks the share example button in the notebook toolbar, a new tab opens showing a rendered copy of the notebook. It's not clear from that feedback alone that the notebook is now shared with other users as an unreviewed example.

Possible fixes:

• Show a toaster popup explaining what happened
• Open a new browser tab pointing to the Examples tab on the notebook dashboard page and highlight the example shared/updated

[parente]

Duh. I duped my own issue #14.