Add internationalization foundation.

Adds the i18next module to implement internationalization on both the client and server side of the app, using a common translation file. 
Using the added functionality, the nav view and template are now localized to abstract the terms for "Project" and "Task".
Adds the gunt-jsonlint module to validate the JSON translation files, since they can get large and complicated.
Server-side implementation is not yet tested in this set of changes.
Having two defined express.customMiddleware (here + config/auth.js) probably won't work - I'd expect them to clobber each other. This looks like a potential workaround: http://stackoverflow.com/questions/21566912/modify-response-header-with-sailsjs-for-implementing-hsts