Remove migration that refers to a nonexistent column

Migrating from scratch hits a snag at this migration, which tries to
drop a column which is referred to nowhere else. I think this is fine
(perhaps I should have just used rake db:schema:load) but may as well
clear this out.
Add some files necessary to run on Heroku

Since Heroku recommends Unicorn, add config file for that.
Since DiffUX depends on redis, add an initializer to configure sidekiq
in that environment.
Since Heroku needs a Procfile to know what to do, add one.
Add rails_12factor gem in production

Heroku requires this gem, because the app must serve its own assets (and
this is disabled by default in Rails 4). It also improves logging
capabilities on Heroku.
Add heroku-multi-buildpack file for phantomjs

Since Heroku is a Read Only filesystem you need to download all the
stuff you'll need at slug compilation time. So the lazy phantomjs
downloading of the tarball won't work.

Fortunately, someone has done the work of making a package that we can
use to fetch phantomjs and include it at compile time. A subsequent
commit will configure the phantomjs gem to use it at the correct path.
Add PhantomJS shim to run on Heroku

I wish there were a way to provide a simple path to a PhantomJS
executable. But it requires a bit of implementation detail as the
PhantomJS gem selects the first usable platform.

None of the default platforms will be usable on Heroku (because of the
read-only filesystem), so this creates a new platform that points to the
correct executable, which has already been installed.
Apparently English is an evolving language

And misspellings like this are okay now.

http://english.stackexchange.com/a/69710
Fix Phantomjs platform methods to be on Eigenclass
Tell Paperclip to use S3 in production
Add aws-sdk gem

Apparently paperclip doesn't know how to do S3 otherwise.
Add Heroku manager which will do black magic
Teach snapshot comparator to find images in different places

In development => images are on local disk => use image.path
In production  => images are on s3         => download image.url

(Maybe we can use the tmp files from the Snapshotter?)
Add README instructions
Improve README a little bit
Remove README errant backticks
Remove migration that refers to a nonexistent column

Migrating from scratch hits a snag at this migration, which tries to
drop a column which is referred to nowhere else. I think this is fine
(perhaps I should have just used rake db:schema:load) but may as well
clear this out.
Merge branch 'master' into heroku

* master:
  Remove migration that refers to a nonexistent column
  Use panels on sweep#show page
  Use panels for each viewport's snapshots on project show page
  Avoid one query in `snapshot#diff?`
  Treat snapshots as pending until they have a diff
  Add loading indicator for Turbolinks
  Add Compass
  Add counter caches to sweeps
  Align one line of code in snapshot model
  Make sure that all snapshot thumbnail cards are same height
  Use Boostrap thumbnail component for snapshot thumbnails
  Put page headers in .page-header element
  Enable Turbolinks
  Remove boostrap JS from application JS manifest
  Remove empty JS and stylesheet files
  Update term-ansicolor 1.2.2 -> 1.3.0, tins 0.13.2 -> 1.0
  Update paperclip gem 4.0.0 -> 4.1.0
  Add "Start new sweep" button to sweeps#index page
  Break up Snapshot#accept!
  Split up SnapshotWorker
  Fix edge case for Snapshot #auto_accept and #diff

Conflicts:
	app/models/snapshot.rb
Revert "Add Heroku manager which will do black magic"

This functionality is specific to my use-case and doesn't belong in the
project itself.
Add README sentence on how to create worker
Add configuration file for Sidekiq

The max concurrency was hitting a limit on Heroku because of the
limitations on Redis.
Merge pull request #48 from ted27/heroku

Add compatibility with Heroku