Setup Pusher for production

## Changes

- add pusher key for production
- turn off debug code for production
- some DRY for initializing Pusher in javascript
- upgrade pusher javascript library to 2.0, host it locally

## Note!

Had to run this command before push to Heroku.. since customized ENV variables can't accessed during assets precompile process... God this thing cost me over 1 hour to debug...

`heroku labs:enable user-env-compile -a knojoe`

[Heroku Labs: user-env-compile | Heroku Dev Center](https://devcenter.heroku.com/articles/labs-user-env-compile)

## Trello Card
https://trello.com/c/5ex9Qpyv