Improve on-boarding

[conorgil]

Currently, the extension on-boarding process after initial install is a web page explaining how the extension works. This is a good start, but an even better on-boarding experience would be to create a wizard in the extension itself to walk the user through how things work.

Ideas:

• have a popup notification on initial install and don't dismiss it until the user clicks it
  • it can have a message "When you visit sites that support 2FA, you'll see a notification like this" or some such wording.
• When the user clicks it, take some action to kick off the tutorial
• change the icon to show the user what each looks like for pages that do and do not support 2FA
• etc

This is a follow in issue from #13

[designedbinary]

Something to explore would be an initial indicator like what tunnelbear does: https://cdn-images-1.medium.com/max/880/1*THSnY3N3grDOIOhrRKwPnw.gif