The `TokenBalance` component now uses the new `useTokenTracker` hook
instead of the `withTokenTracker` higher-order component. The component
was converted from a split container/component to a functional
component so that the hook could be used.
The prop `withSymbol` was removed from a few call sites, as it was no
longer used. An empty string was substituted for any falsy `string` or
`symbol` because that's what the `withTokenTracker` higher-order
component did.
The chosen token in the `send` flow was set from one of two places:
`metamask.selectedTokenAddress` or `metamask.send.token`. The former is
used most of the time, but the latter is used for the 'Edit' button
shown in the upper-left of the confirmation UI.
The send flow will now exclusively use `metamask.send.token` for the
token state during the send flow. `metamask.selectedTokenAddress` is
now only used for the selected token state on the Home screen. This
simplifies the Redux state, as the send token is now in one place
instead of two, and `metamask.selectedTokenAddress` has only one
purpose.
* Move send to pages/
* Fix unit tests
* Finish UI
* Integrate asset dropdown to send actions
* Remove console.log
* Hide asset change during edit
* Enable switch from send token to seand eth
* Enable switching from token to eth when editing
* Fix linter
* Fixing test
* Fix unit tests
* Fix linter
* Fix react warning; remove console.log
* fix flat test
* Add metrics
* Address code review comments
* Consistent spacing between send screen form rows.
* Reduce height of gas buttons on send screen.
* Make send screen gas button height dependent on size of contents.
