Generate models for notification and notification_receipts
Replace em-websocket with 'websocket-eventmachine-server'

Primary reasons for the switch:
[1] As mentioned in "https://github.com/imanel/websocket-eventmachine-server" :
"There are multiple Ruby WebSocket servers, each with different quirks and errors. Most commonly used em-websocket is unfortunately slow and have multiple bugs(see Autobahn tests above). This library was created to fix most of them."
[2] Availability of native extensions
Setup initial client-server websocket handshake