Use symbols instead of strings

ActiveSupport::Concern is used all over Rails
This PR will only create 3 new objects as keys are never recreated and
are not subject to garbage collection.

The strings were being uniquely created and garbage collected. I don't
have any performance numbers but this should be better than all of the
GC.
Making the rake file for tests easier to read.

I'm defining a new class which modularizes how the `rake test` tasks are
defined and invoked.
Adding documentation to the Rails initialization guide. [ci skip]
Improved grammar and replaced 'dbs' slang with 'databases'
Remove deprecated attr_protected/accessible

Rails 4.0 has removed attr_protected and attr_accessible feature in favor of Strong Parameters.
Review AV changelog [ci skip]
Merge pull request #11149 from strzalek/remove-protected-attrs

Remove deprecated attr_protected/accessible
Asking user to declare post resource in guide [ci skip]
Merge pull request #11127 from jetthoughts/ask_user_add_line_to_routes_in_guide

Asking user to declare post resource in getting start guide
Remove deprecation warning from AttributeMethodsMatcher
Remove depreacted finders

They were deprecated in 4.0, planned to remove in 4.1
Merge pull request #11150 from jetthoughts/remove_depr_message_for_attribute_method_matcher

Remove deprecation warning from AttributeMethodsMatcher
adding additional plugins for debugging [ci skip]
Fix indentation
Merge pull request #11153 from strzalek/remove-ar-deprecated-finders

Remove depreacted finders
Fix rake test_sqlite3_mem

Clearly nobody uses this except me. It's fast people!
Fix test

Oops. We need to estalish/remove the connection in the setup/teardown,
else it messes with the fixtures.
Apply default scope when joining associations.

For example:

    class Post < ActiveRecord::Base
      default_scope -> { where published: true }
    end

    class Comment
      belongs_to :post
    end

When calling `Comment.join(:post)`, we expect to receive only
comments on published posts, since that is the default scope for
posts.

Before this change, the default scope from `Post` was not applied,
so we'd get comments on unpublished posts.
Fix layouts and rendering guide example using flash.now instead

Thanks @lintzchiang. [ci skip]
Merge pull request #11104 from drewda/patch-1

Adding additional plugins to debugging guide [ci skip]