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
Remove useless sudos
BUGFIX: fix math & unit when checking disk space
FIX: New counts were taking into account muted categories
FEATURE: add a banner when read-only mode is enabled
BUGFIX: this fixes a chrome bug... I would laugh if I wasn't already
crying.
Version bump to v0.9.8.6
Add a Staff category. Have a topic for assets in the Staff category. Move admin quick start guide to Staff category. Quick start guide is not invisible anymore.
Revert "Add explicit confirm button text on post abandon"
BROKEN

This reverts commit 6bab39b9cd9b320a22add268704ea2f379f955f5.
BUGFIX: don't force load drafts when composing.
It will still be there after post is made.
Don't tell you that you successfully flagged a topic.
Version bump to v0.9.8.7
Updated Japanese locales
Revert "Use symbols instead of strings in order clause"
Breaks 1.9.3 compat

This reverts commit 09a2d9e12c56dc0358901fd3aea2684ca0d27b0c.
clarify remove comments in front of email lines
BUGFIX: couldn't upload backup on OSX

--B is not a valid df option on OSX
Optionally allow discourse to create new topics from email.
Refactor and clean up New-Topic via Email

With the new email_in admin configuration setting, emails to the email_in_address fetched via POP will now be processed and posted as new topics to the forum.

With the email_in_min_trust you can control the trust level the user needs to have at least to be able to post an email as a new topic.

Also contains tests for the email-in feature and minor clean ups
Add Email-In-Per-Category

 - allow the configuration of an inbox-email-address per category
 - post emails to that email into that category instead of global

 - Adds UI for configuration
 - Adds Documentation for configuration
 - Adds Tests for new feature