Client: Apps: show loading time estimate

[john-light]

Is your feature request related to a problem? Please describe.
When an app is loading, there is a "syncing data..." indicator, but no hint as to how long loading may take.

Describe the solution you'd like
Given the wide variation of loading times, it would be nice if we could provide an estimate about how long loading may take.

Describe alternatives you've considered
As a stopgap, an info icon on the loading indicator that when you click it says something like "This could take anywhere from one minute to an hour depending on how old the organization is and how much data there is to load."

Additional context
Add any other context or screenshots about the feature request here.

[stellarmagnet]

Yes, good call on this.

I feel like we should also put the "syncing data" near the top of the page

[sohkai]

We've discussed with @dizzypaty that this is already possible to guess, based on the number of blocks you're trying to sync. It _may_ come in 0.8, or will come soon in a 0.8.x release.

[dizzypaty]

Syncing indicator

Appearance

We applied the new visual style to the toast component and used it as a base to communicate feedback about the data syncing process, including a time estimate for completion that will vary based on the block number its syncing from.

Positioning & behavior

This feedback component will include an animated spinner and a line of text. Its position will be exactly the same as the toast component. In the unlikely event that a toast is triggered while syncing data, we will stack these elements vertically (following the current toast behavior).

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• Fixes #879
• Design assets here.