Add a design system (#34)

* Add theming system

* Add standard Button control and update RadioButtons

* Unify radiobutton with design system

* Update debug screen to have multiple views

* Add ToggleButton

* Update error controls to use design system

* Add typography to <Text> element

* Move DropdownButton into the design system

* Clean out old code

* Move Text into design system

* Add 'inverted' color palette

* Move LoadingPlaceholder into the design system

src/view/screens/NotFound.tsx

@@ -1,7 +1,7 @@
 import React from 'react'
 import {Button, View} from 'react-native'
 import {ViewHeader} from '../com/util/ViewHeader'
-import {Text} from '../com/util/Text'
+import {Text} from '../com/util/text/Text'
 import {useStores} from '../../state'
 
 export const NotFound = () => {