New navigation model (#1)

* Flatten all routing into a single stack

* Replace router with custom implementation

* Add shell header and titles

* Add tab selector

* Add back/forward history menus on longpress

* Fix: don't modify state during render

* Add refresh() to navigation and reroute navigations to the current location to refresh instead of add to history

* Cache screens during navigation to maintain scroll position and improve load-time for renders

src/view/screens/NotFound.tsx

@@ -0,0 +1,13 @@
+import React from 'react'
+import {Text, Button, View} from 'react-native'
+import {useStores} from '../../state'
+
+export const NotFound = () => {
+  const stores = useStores()
+  return (
+    <View style={{justifyContent: 'center', alignItems: 'center'}}>
+      <Text style={{fontSize: 20, fontWeight: 'bold'}}>Page not found</Text>
+      <Button title="Home" onPress={() => stores.nav.navigate('/')} />
+    </View>
+  )
+}