Multi-peer connectivity support

[oleganza]

1. To push tx directly to a recipient (e.g. while in roaming or where 3G connection is poor).
2. To enable 2-factor signing (e.g. from a phone and from a laptop).
3. Enable in-person contract signing without intermediary app or service.

Some Android wallet I heard support that, so if possible we should too using raw Bluetooth (to be compatible), not only Apple's MultipeerConnectivity framework.