Move config/ folder to server/config/

[leopiccionia]

From the Feathers/Express server point of view, the steps described here are enough to implement this feature. Nonethewise, the Feathers CLI generators expect a config folder in project root, and would re-create it if it doesn't exist.

This feature is, therefore, not a limitation of this specific boilerplate, but would certainly enhance this. I should probably give feathersjs/feathers#987 a try.