Notify user when long analysis completes

Notifying users when a long analysis (ex. more than 15 seconds) completes would be an alternative to the more complex solution of implementing a progress bar for analyses #284.

> **ssmagula:** User starts a process. Sometimes it takes seconds, sometimes hours, and currently there's no feasible way to predict how long it will take. Users don't want to "babysit" the process (actual term I've heard used often) and would like to move on to some other task. So, to serve this goal: the indeterminate spinner is displayed, and beneath it text such as "This may take some a while
Get notified when blorf is ready [Notify me]" T
> * That way, users can wait as long as they're happy to sit and wait, but can hit the [Notify me] button when they grow tired of waiting.
> * The notification could be a toast message (probably best in Trace Viewer context), but in other contexts could be an email/sms/audio alert

Alternative to: #284

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CC: @arfio @ssmagula

Start by reviewing issue #284 and the Trace Viewer analysis flow described here. Clarify whether the first implementation is limited to an in-app notification or also includes email, SMS, or audio alerts. Done means users can opt in while a long analysis runs and receive a notification when it completes.

Written by the indexing model from the issue text.