Prepare for Heroku deployment

Commit API key to deploy to Heroku

Signed-off-by: Marcel Oomens <Marcel.Oomens@cromido.org>
Changes to the handling of API key

API key is read from (1) query string parameters or (2) from environment variable. If no API key is present the server returns 400 (bad request).

Signed-off-by: Marcel Oomens <Marcel.Oomens@cromido.org>