First time visiting site should mark everything read

[timwis]

Since there's no lastRead property in localStorage, it shows every conversation as completely unread. Instead, it should show them all as "read" until a new message comes in.

Ideas:

• If lastRead property doesn't exist in localStorage, set every conversation's lastRead to the current timestamp (but the subscription doesn't know about all the conversations)
• Set a new property in state called firstRead and have the view also compare to that timestamp. It would only be set on the first visit to the page.