A new page has been created for viewing assets. This replaces the old
`selectedToken` state, which previously would augment the home page
to show token-specific information.
The new asset page shows the standard token overview as seen previously
on the home page, plus a history filtered to show just transactions
relevant to that token.
The actions that were available in the old token list menu have been
moved to a "Token Options" menu that mirrors the "Account Options"
menu.
The `selectedTokenAddress` state has been removed, as it is no longer
being used for anything.
`getMetaMetricState` has been renamed to `getBackgroundMetaMetricState`
because its sole purpose is extracting data from the background state
to send metrics from the background. It's not really a selector, but
it was convenient for it to use the same selectors the UI uses to
extract background data, so I left it there for now.
A new Redux store has been added to track state related to browser history.
The most recent "overview" page (i.e. the home page or the asset page) is
currently being tracked, so that actions taken from the asset page can return
the user back to the asset page when the action has finished.
* Remove unused sendWarnings
The send warnings state and associated component is no longer used
anywhere.
* Remove unused subtitleParams
The `subtitleParams` SendHeader prop was being ignored. It has been
removed, along with associated selectors and tests.
* 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.
