Feat/config path from package.json

[jraut]

Hello,

This pull request is created because of feathersjs/feathers#987

It lets the CLI use a custom config folder.

Based on the discussions on the issue, the following changes were made to generating a new project

- When creating a project, the package.json is created with a property for a config directory
- The value is read from NODE_CONFIG_DIR env variable since it is used by default
- If the value is not set, it is set to config/ (the current hardcoded value)

Generator uses this new customizable value. It falls back to config/ on run time to maintain backwards compatibility.

[daffl]

I fixed the tests and made the release. Thank you for adding this!