This fixes the linter's warning that Hooks must be run in order each time.

* In App.tsx
  - move the conditional that returns suspense if the path is oauth/callback to the end of the component after all hooks, rendering either suspense or the normal component.
  - move handleApproveSampling and handleRejectSampling functions down below all the hooks for clarity. There are a lot of hooks so finding the end of them is a scroll, and these function constants aren't referenced until the rendering section below anyway.

Author: cliffhall