Move i18n messages out of subdir
Compute locales from .json files and clean-up app

This computes the all of the app's supported locales by looking at the "i18n/"'s JSON files.

This also cleans up the app.js Express app code a bit.
Add basic utils for middleware and routes
Add `intl` middleware
Merge pull request #4 from ericf/i18n-msgs-http

Refactor i18n messages organization and use HTTP content negotiation