Use dotenv for development

To simplify the ease of environment loading in development mode, use
dotenv with a sample file
Smarter Pusher config

We do not necessarily want to force users to specify Pusher config stuff
right away. Just log a warning for them to do so later should they
choose.
Only load ffaker when running db:populate task
Update Pusher javascript to pull the correct Pusher key
Return developer instance, not result of save call