Create rake task to check if database exists (#90)
Create rake task to check if database exists (#90)

Create the rake task `rake db:exists` which returns `1` or `0` if the
database already exists or not. This is useful when deploying to a
server and determining if we need to run `setup` or `migrate` on the
database.

Fixes: #83
ephracis/stoffi-web,ephracis/stoffi-web,ephracis/stoffi-web,ephracis/stoffi-web