Onboarding gifs/messages

[cameron-toy]

Add some quick one-time onboarding gifs/messages to explain how to use the extension.

Examples:

• Opening a dashboard for the first time displays a gif on the dashboard showing how to drag an output from a notebook on to the dashboard until the user adds an output.
• Adding a second output displays a gif illustrating options for navigating the dashboard.
• Dragging an output already on the dashboard the first time displays a gif showing how to switch between free/tile/present modes.

[juliahuynh]

Potential GIF for onboarding

• subject to change depending on how workspaces are automatically rearranged upon dashboard launch
  

[juliahuynh]

Updated GIF created with Adobe Animate: