Migration CLI

[evantahler]

At work (grouparoo/grouparoo#1631) we had the need for a CLI to manually step up and down migrations. Since this plugin allows for multiple migration directories, a custom CLI tool was needed. Perhaps we can port the linked tool into this plugin.

[evantahler]

It's now easier to use ah-sequelize-plugin to create a migrator utility - https://github.com/grouparoo/grouparoo/blob/main/core/bin/migrator