added pusher node

Added nodes for pushing events to Pusher service and subscribing to
notifications from channels/events
merged html and js

merged into a single html and single js file
fixed copyright typo
added credentials proper handling
lower case node name and pusher in fixes

fixed lower case node name and replace input node to ‘pusher in’
fixed credentials to never show up in the flow

removed credentials from the defaults section in pusher.html, added
oneditprepare to read them back from credentials.json when edited
Merge pull request #56 from hdoukas/master

added pusher node