* First pass at handling API failure.
* Bity saga logic upgrade.
* Reusable response.ok logic. Small optimization to array join.
* Flow fixes.
* Streamlined some error handling, moved types.
### Re-implements:
* min/max validators on initial currency swap selection
* polling of order status
* timer that persists across refreshes via localStorage (computed based on `createdTime` and `validFor` amount)
* swap persists across refreshes once order is created.
* various type refactors
### New additions:
* *SimpleButton* (can be PRd separately on request)
* clear loading state after order create (via SimpleButton and font-awesome)
* buffers for non-BTC swaps (bity does not actually accept 0.01 BTC worth of ETH as they claim they do in their JSON response, so a magic number of 10% is added to the minimum).
Bryan Fillmer
Daniel Ternyak