Bis2001 use single host

This change is for BIS2001 https://podio.com/bitzesty/bis-phase-2/apps/stories/items/1

The app will run on single domain so we have to mount frontend app at / and backend app at /backend

Things that could be improved:

* figure out why /backend redirects to /backend/backend/users/sign_in (looks like devise related bug?)
* possibly add nginx directive that rewrites /api calls to /backend/api
* update to capistrano-rails 1.1.1 once it's actually released and get rid of custom asset  tasks