Add db seeding functionality for development

[spencern]

Create a new command seed that will seed the mongo database with fake products, orders, tags etc.

Currently, this functionality lives in https://github.com/reactioncommerce/reaction-devtools,

This issue is blocked by two issues:

1. Removing the Meteor dependency from file-collections
2. Abstracting the seeding functionality of devtools into an npm package: Migrate the db seeding functionality of devtools to an npm package reaction-devtools#18

This command may need to take a --dbport or similar flag to determine how to access the correct database.

Additional functionality could include passing a "size" flag (e.g. reaction seed --size large) or passing in specific parameters for different data sets - e.g. reaction seed --products 1000 --tags 200 --orders 5000 or something similar.

Questions

1. Are there any major drawbacks to doing it this way?
2. How else could we accomplish this functionality?
3. Is this the correct place for this functionality or should it live in separate CLI command?

Acceptance criteria
I can run the following command to seed a mongo database with a default set of product data

reaction seed

[spencern]

@jshimko suggests that we could export a mongo db with the seeded data as a temporary, easier solution.

[spencern]

@kieckhafer has created a data set that he will publish somewhere that contains a great set of starter data. Closing this issue in favor of that solution for now.