The "closing soon" bubbles were introduced in #406, and the "falling
back" bubbles in #500. However, these bubbles are part of the cached
card and so as time passes, the relative time doesn't change unless
the card is touched.
This PR introduces a stimulus controller for bubbles, which takes care
of:
- making the bubble visible during the reminder period
- calculating the relative number of days until entropy kicks in
- rendering appropriate text around the day count
ref: https://37s.fizzy.37signals.com/collections/693169850/cards/999009091
Stanko K.R.