Add a default migrationsDirectory to box.json

[dbelanger]

We're using commandbox-migrations to apply migrations that aren't in the default migrationDirectory and rather than enter the new directory every time we use a command, I've made the command line the override.

By adding this key to the cfmigrations section of the box.json, we're also making it more obvious to those who use it where there scripts are going to be. This is also handy if we need to change it in another environment.

I also refactored some repeated code from the actions to the base class.

This change shouldn't affect existing users.

[elpete]

This is a really nice addition. Thanks!

[elpete]

Published as 3.1.0