Welcome Popup for New Users

[cwitkowitz]

Should we have a welcome window that opens upon launch for new users? The window could include information about adding tokens and using the application, with the intention of mitigating common friction points.

[cwitkowitz]

We also talked about adding "pages" to the welcome popup which describes (and potentially visually highlights) each widget and major feature of the application.

[cwitkowitz]

I merged PR #352, but before closing this issue, let's make sure other team members think the welcome text is sufficiently descriptive for new users.