Bug 1048717 - [Messages][Refresh] Display call button at the header of single recipient thread. r=schung

Also there are cases when Dialer activity rejects numbers that dont match to number pattern set in manifest. So when user taps on Call button nothing happens. It happens to me with senders that equal to string (I receive operator SMS with sender === 'Fehlerinfo'). So as temporal measure I can add 3rd check here with regex taken from Dialer manifest, but in long term I think there is a chance that we use mozTelephone.dial directly to resolve bug https://bugzilla.mozilla.org/show_bug.cgi?id=1032273