Keep track of which strava activities have been added

[aaron-schroeder]

Update 4/6: removing from 0.1 milestone and putting back into the idea cauldron.

Old notes

• Strava activity view: check if activity is already saved to the app #53
• Strava list view: Show which activities are already saved
• Batch save task: do not save activities that already exist in db
• Show any strava activities that are similar to db activities, even if the strava id doesn't match.
  • To test this, view my older strava acct's activity list in my local environment. It should highlight strava activities that bear similarities to ones that already exist in the database (from my newer acct).
  • This now happens on the strava activity list view (in a primitive way)
  • Still needs to happen when viewing an activity detail

[aaron-schroeder]

Not sure where this fits in the new universe of DF. Removing from the 0.1 milestone for now.