Convert ShapeShift modal to store (#4035)

* WIP

* WIP store

* Store in-place

* WIP tests

* Store completed

* Expand option tests for events

* Fix & test for errors found in manual testing

* Add missing @observer (rookie mistake)

* Fix intl formatting error (completed step)

* Pass store to ErrorStep, test all stages for components

* Add warning messages (e.g. no price found)

* Fix typo