Finish new Message component, integrate into application

Also:
- New schema version 8 with video/image thumbnails, screenshots, sizes
- Upgrade messages not at current schema version when loading messages
  to show in conversation
- New MessageDetail react component
- New ConversationHeader react component

ts/components/conversation/SafetyNumberNotification.md

@@ -0,0 +1,25 @@
+### In group conversation
+
+```js
+<util.ConversationContext theme={util.theme}>
+  <SafetyNumberNotification
+    i18n={util.i18n}
+    isGroup={true}
+    contact={{ phoneNumber: '(202) 500-1000', profileName: 'Mr. Fire' }}
+    onVerify={() => console.log('onVerify')}
+  />
+</util.ConversationContext>
+```
+
+### In one-on-one conversation
+
+```js
+<util.ConversationContext theme={util.theme}>
+  <SafetyNumberNotification
+    i18n={util.i18n}
+    isGroup={false}
+    contact={{ phoneNumber: '(202) 500-1000', profileName: 'Mr. Fire' }}
+    onVerify={() => console.log('onVerify')}
+  />
+</util.ConversationContext>
+```