Bug 1037232 - Display an error message for unverified accounts. r=arthur...

...cc
The login button will be displayed again only if the login panel is displayed, which only happens [when logged out of FxA](https://github.com/guilherme-pg/gaia/blob/35344224d8b74fdefdb70be75581c4f319fc3255/apps/settings/js/findmydevice.js#L22). So you can't log out from FMD's panel, but if you log out from FxA's panel, the button will be displayed again.