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.
* Changed max button to checkbox, disabled input if max mode is on, recalculate price according to gas fee if max mode is on
* Disabled insufficient funds message in the modal if max mode is on, displays proper amounts in modal when max mode is on, sets the send amount according to custom gas price after gas modal save, resets the send amount after resetting custom gas price
* Disabled max mode checkbox if gas buttons are loading, refactored gas-modal-page-container
* Implemented new max button & max mode message. Moved insufficient funds error to underneath the send amount field
* Fixed existing integration test to pass, created new tests to ensure send amount field is disabled when max button is clicked and the amount changes when the gas price is changed. Refactored some components
* 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.
