Tutorial: MT3: Sporadic Tutorial-like UI Hints and Prompts

[BorisJov]

Add sporadic tutorial-like hints and prompts to occasionally invite the user to do something (e.g. add title).

From time to time the user could be prompted with a message in-UI that they should do or look at something. Examples:

• 'login to sketchfab': a prompt to register account and log in to Sketchfab, if they haven't done so already.
• 'add title' fly-out inviting to: open title tab, add title, add description.

List of items still needs to be discussed.