remove exception notification
add dotenv

only for development. hopefully, heroku won’t complain
use dotenv

- add `.env.example` with the minimum configuration required
- make email load it’s configuration from `.env`
- make pusher load it’s configuration from `.env`
- make secret_token load from env
- ignore `.env` and remove old `.gitignore`s
use `rails_12factor`
require dotenv only if it's defined

so that heroku doesn't complain and we don't use dotenv on production
Merge branch 'master' into heroku
specify ruby version in Gemfile

and ignore local ruby version `.ruby-version`
upgrade puma
add `foreman` and Procfile
simplify `AdminConstraint`