Account switcher (#85)

* Update the account-create and signin views to use the design system.

Also:
- Add borderDark to the theme
- Start to an account selector in the signin flow

* Dark mode fixes in signin ui

* Track multiple active accounts and provide account-switching UI

* Add test tooling for an in-memory pds

* Add complete integration tests for login and the account switcher

jest/test-utils.tsx

@@ -4,20 +4,19 @@ import {GestureHandlerRootView} from 'react-native-gesture-handler'
 import {RootSiblingParent} from 'react-native-root-siblings'
 import {SafeAreaProvider} from 'react-native-safe-area-context'
 import {RootStoreProvider} from '../src/state'
+import {ThemeProvider} from '../src/view/lib/ThemeContext'
 import {mockedRootStore} from '../__mocks__/state-mock'
 
-const customRender = (ui: any, storeMock?: any) =>
+const customRender = (ui: any, rootStore?: any) =>
   render(
     // eslint-disable-next-line react-native/no-inline-styles
     <GestureHandlerRootView style={{flex: 1}}>
       <RootSiblingParent>
         <RootStoreProvider
-          value={
-            storeMock != null
-              ? {...mockedRootStore, ...storeMock}
-              : mockedRootStore
-          }>
-          <SafeAreaProvider>{ui}</SafeAreaProvider>
+          value={rootStore != null ? rootStore : mockedRootStore}>
+          <ThemeProvider theme="light">
+            <SafeAreaProvider>{ui}</SafeAreaProvider>
+          </ThemeProvider>
         </RootStoreProvider>
       </RootSiblingParent>
     </GestureHandlerRootView>,