Add dummy Posts resource and home page

Summary:
* Posts
  * Add angular-resource
  * Add simple data service for posts
  * Remove the inline HTML dummy post data
  * Add a ng directive for single post item preview in the list view
  * introduce API_URL constant for backend url
* add a simple home page
* change routes correspondingly ('/' -> homepage, '/posts' -> posts)
* change require style in app.js

Test Plan: Just checkout the /posts url

Reviewers: rjmackay, seth, shadowhand

Subscribers:
First version of OAuth2 signin/signout feature

Summary:
* add simple sign in form and use OAuth2
  * use a http interecptor for catching unauthorized http responses
  * add a ng service for the authentication process
* signin/signout button (as a ng directive)
* assumes that there is a dummy backend (configure the backend url in app.js) which allows
  * to sign in with OAuth2 Resource Owner Credentials Flow
  * to fetch posts (only when signed in / with a valid access_token)

Test Plan:
* try to open /posts without beeing signed in
* then sign in and try again

Reviewers: rjmackay, seth, shadowhand

Differential Revision: https://phabricator.ushahidi.com/D323
change 'log in' to 'sign in'
WIP: protractor setup
WIP: protractor setup
WIP: protractor setup
WIP: protractor
WIP: protractor
WIP: protractor