fix(avatars): redirect unverified users to confirm screen

If an unverified user visits the avatar page we tell them to confirm and resend the email.

@shane-tomlinson r?

Fixes #1662.
Could we do something like load the real FxaClient and create a mock function for every method on the instance? IIUC, all of the methods return a promise, so we could have each method return a promise that resolves to "true" by default, or something similar?