Optimize events emitted by Wallet.js and WebRTC.js

Some changes:
- removed automatic refresh on wallet store 
- changed some event names to make them more clear
- networking code refactor to enforce DRY
- removed unused or redundant events (pubKeyRingUpdated, open)
- removed unnecessary $digest calls
- reduce calls to insight REST and socket APIs in address generation

fixes https://github.com/bitpay/copay/issues/325
This also partially addesses https://github.com/bitpay/copay/issues/294