Posts: add preview ngDirective and dummy data

Summary:
* Add a ng directive for single post item preview in the list view
* add dummy json post data in posts controller
* change routes correspondingly ('/' -> posts, '/posts' -> posts)
* change require style in app.js

Test Plan: Just checkout the /posts url

Reviewers: seth, shadowhand, rjmackay

Reviewed By: rjmackay

Subscribers: rjmackay

Differential Revision: https://phabricator.ushahidi.com/D321