added `pusher-client`

see https://github.com/pusher/pusher-ruby-client
bandango.yml now needs also business_token (to subscribe to events)
renamed to bandango_sani_syncable
added PusherWorker

it triggers SaniGetWoker whenever is triggered `new_transaccion` on
pusher server
added pusher.yml
added pusher initialiser

it assures only one PusherWorker is running
Merge branch 'master' into stable