[alpha]mobile: app should disable listening

[Roasbeef]

Reported by many users: if they have another LN app installed on their phone, then ours will crash once it finishes syncing. This is due to the fact that the other applications are tyring to listen on the default p2p port (9735). As this is a mobile app, we don't really need to be listening at all. As a result, we should start lnd with the following flag:

      --nolisten                                              Disable listening for incoming peer connections