We don't need to store the current UI type as a global. We're already
using the `getEnvironmentType` helper function throughout the UI, so
we'd might as well use that instead of this global state.
Two tabs have been created on the home screen: 'Assets' and 'History'.
This tabbed view is shown only on small screens (e.g. in the popup).
The fullscreen view is unchanged.
The toggle-able left sidebar no longer exists, so some 'sidebar-left'
specific code and styles have been removed. The button in the menu bar
has been removed as well.
The 'History' title of the transaction history is now redundant when
where are no pending transactions, so it as been conditionally hidden.
A passthrough for `data-testid` has been added to the Tab component for
convenience in e2e tests.
This commit updates the existing _Connected Sites_ section to a modal using
the `Popover` component. This will serve as a base for the new modal design.