Various cleanups to Ubuntu installation instructions:

* Avoid editing /etc/apt/sources.list add nginx repo, instead create
  /etc/apt/sources.list.d/nginx.list

* Avoid editing /etc/nginx/nginx.conf, instead put server_name_hash_buckets
  setting into discourse.conf

* Proper-case Discourse when it is referring to the product name, so that all
  the lowercase references are to the user created during the installation
Address @Supermathie's concerns in PR1430
Fix Post-rendering bug

Ember.Handlebars.normalizePath was being called with an object as
argument which caused it to error out.
also wrapped the return in a SafeString, so the html will not get
escaped again.
Disallow auth callbacks in robots.txt
Delegate :username rather than using a class method.

This is just a little cleaner?
Page title includes page number for web crawlers
BUGFIX: groups page wasn't working
BUGFIX: could not save user's preferences when categories where watched/tracked/muted
FIX: Accept HTTPS or HTTP urls on redirect
FIX: Allow click tracking to work with different origins
FIX: Incorrect string match
FIX: When embedded, don't show button at the top unless there are more than 10 posts.
BUGFIX: emoji's url were relatives (was breaking the wordpress plugin)
BUGFIX: inline spoiler for text, block spoiler for images
BUGFIX: do not pull images we already host locally
message bus update
* supports new /global/ cross sites bus
* supports last_message
FEATURE: Automatically force a full refresh between pages if assets change
Source DB config more cleanly, fixes issues with socket in prd
FEATURE: automatically update site to latest version of assets
if a user neglects to move around the site it will prompt to do so 2 hours in
update copy a bit