Use git URL for ink_step gem in Gemfile

See merge request INK/ink-api!12

Add postgres/ to .gitignore

See merge request INK/ink-api!10

Update Docker instructions

See merge request INK/ink-api!13

Use Docker volume for postgres data?

See merge request INK/ink-api!14

docker volume create --name=pgdata

`docker-compose.yml` contains a volume mapping from  `./postgres` to `/var/lib/postgresql/data`, which creates a "postgres" directory that needs to be ignored by version control.

Recipe step presets created from process steps. Simple recipe controller action for increased efficiency/lazy loading. Updating tests to accommodate XSweet changes