Google Calendar integration

[apdarr]

Using Google OAuth, we should have the ability to from the app:

• Create a calendar that puts all of our runs on it.
• All plans are added to this calendar.
• User can choose the time of day they typically run, which directs the time those are placed on the calendar.
• If the user moves an plan's activity to a different day, that Google Calendar event should also update.
• Repeated plans should use the same calendar link. Use case: a user shouldn't have to re-share a new calendar every time they start a training plan. They should be able to have 1 Google Calendar that we select or create for them, and then runs are added to that calendar.
• Calendar syncing should be presenting to the user when we create a training plan.