Added jinja filters

Added following jinja filters:
* format_date
* time_since
GAE specific fix for PRAW
Added posted_date for easier ndb query
Fix to import datetime
Updated for Post query
Added basic views, URLs and templates

Added/updated following views and corresponding URLs and templates:
* home
* authorize
* user_profile
* me
* post_daily3
* logout
Customized 404 page
Added basic CSS and JS components