Status-react: Chat screen does not look like design

[jarradh]

• [ ] in many designs the top bar colour does not change with header, instead it is semi-transparent black, i saw @alwx do this correctly in past, we should make this uniform
• [x] dates and messages unread are missing?
• [x] horizontal line seperator between chat sessions is missing
• [x] there should be grey empty area beneath end of chat screen if screen real estate is available

[alwx]

Finished.
Transparent StatusBar will be available later (I've submitted a PR to React Native with this fix: https://github.com/facebook/react-native/pull/10185)

[jarradh]

nice work committing upstream and getting accepted! woo!