Fix and simplify state management of Instant Purchas setting
Add Instant Purchase check to Watch page
Merge Max Purchase Price and Instant Purchase into one section
Wording still not finalized.
Add Instant Purchase setting names to constants
Support USD for Instant Purchase
On Settings page, use constants for new Instant Purchase settings
Convert Instant Purchase Maximum setting into FormRow
Update wording of Instant Purchase option and add helper text.
Wording still not final.
On Settings page, get Instant Purchase settings via selector
Update CHANGELOG.md
