Spell "explicitly" correctly

* yay spelling!
Add i18n-tasks for missing/unused translations

* i18n-tasks looks for missing *or* unused translations
* Add config file to ignore certain i18n keys (eg: activerecord) which
  are used as defaults but not explicitly in views or helpers
* Remove code to raise in test env when there are unused translations
Add normalize-rails
Specify newer Bitters version in Gemspec
Be clear that the user must run the setup script

This should help with confusion such as this report:

https://github.com/thoughtbot/suspenders/issues/387
v1.16.0
Generate spec/support/i18n.rb file

* Enable using just `t` (not `I18n.t`) in specs which was introduced in
  7ea5176 and removed in eaf7de1
* Add spec to ensure i18n support file is added
Set `en.titles.application` to App Name

* Gives developers that are unfamiliar with Caleb's `title` gem a nice hook to
  get started with
Do not ignore errors when checking for foreman

The `&>` syntax is not valid sh. Instead of changing it to valid sh
syntax (`2>&1 > /dev/null`), we can instead drop the `&` entirely.

If `command` prints to stderr, `foreman` may or may not be installed. In
this case the user will want to know that there was an error; telling
them that `foreman` is not installed masks the error, making debugging
trickier.
Raise unpermitted parameters in test environment

Unpermitted parameters were being raised in the development environment
but ignored in the test environment. That can cause specs to pass even
though performing the same steps in development will fail.

This change raises unpermitted parameters in all environments for
parity.
Raise on missing translations in test

Although we're generating a separate `spec/support/i18n.rb` file for i18n
(4d30479c3750ad5ce708cbf03ab8a58d484f2e8a), we're
once again **not** failing specs when a translation is missing.
Add normalize-rails to application.css.scss
Generate rails_helper, not spec_helper

RSpec 3.x introduces a `spec/rails_helper.rb` file
which contains all dependencies necessary to run specs that need Rails.

https://www.relishapp.com/rspec/rspec-rails/docs/upgrade#default-helper-files

Achieves the goal of "Documenting Explicit Dependencies Through Tests":

http://robots.thoughtbot.com/document-explicit-dependencies-through-tests

* Move Rails-specific things to rails_helper.rb.
* Require spec_helper.rb from rails_helper.rb.
* Remove duplication across files.
* We do not need to require "spec_helper" manually.
  It is required for us in `.rspec`:

    --color
    --warnings
    --require spec_helper
Generate a Rails 4.1.6 app
v1.17.0
Improve generated bin/setup

* Make script idempotent.
* Fail fast with install messages and non-zero exit status.
Remove unnecessary check for directory existence

`mkdir -p` will no-op if the directory already exists.
Use `uncomment_lines` Thor helper
Ignore the entire /tmp directory

This ignores the generated `tmp/heroku_commands` file instead of just the
`tmp/dummy` app.
Chome considers port 6000 unsafe

See http://superuser.com/questions/188058/which-ports-are-considered-unsafe-on-chrome