Amethyst v0.15.1: Zaps

Few Things first:

1. This is an early release. You can send and receive zaps with a fixed amount (1000 sats) and see those received zaps in user's profile and in your notifications. Sending is a bit too slow. More options will be coming.

2. The receiver MUST use Zap-supported lightning address setup to work. Otherwise, you would just send a lightning tip and the amount will not update on the screen.