Add default .raise_in_transactional_callbacks option to template

Correctly determine if migration is needed.

Improve custom configuration

Related with #11795.

Update `ActionController::Parameters` to be more secure on parameters handling

Add missing AS require

`strip_heredoc` method is defined on active_support/core_ext/string

1. Hashes can be assigned
2. We don't need a special level anymore

The method chain only works in the top level.

If users need a second level they need to assign a OrderedOptions to the
key:

    config.resque.server = ActiveSupport::OrderedOptions.new
    config.resque.server.url = "http://localhost"
    config.resque.server.port = 3000

[Rafael Mendonça França + Carlos Antonio da Silva]

Conflicts:
	actionpack/lib/action_controller/metal/mime_responds.rb
	actionview/lib/action_view/vendor/html-scanner/html/sanitizer.rb
	activerecord/lib/active_record/type/value.rb

Small grammar fix in pluck description

Do not depend on queue_classic on JRuby

4.2 Release Notes pass [ci skip]

[ci skip] config.active_record.errors_in_transactional_callbacks -> config.active_record.raise_in_transactional_callbacks

[ci skip] Update plugin doc with the latest rails

[ci skip] Removed unnecessary word from Getting Started

[ci skip] config.active_record.errors_in_transactional_callbacks -> config.active_record.raise_in_transactional_callbacks

Ruby 1.9.3 does not implement Hash#to_h, so we can't call `super` on it.

* `each`
* `each_pair`
* `delete`
* `select!`

This is to make sure that `permitted` status is maintained on the
resulting object.

I found these methods that needs to be redefined by looking for
`self.class.new` in the code.

* extract!
* transform_keys
* transform_values

`ActionController::Parameters#to_h` now returns a `Hash` with
unpermitted keys removed. This change is to reflect on a security
concern where some method performed on an `ActionController::Parameters`
may yield a `Hash` object which does not maintain `permitted?` status.
If you would like to get a `Hash` with all the keys intact, duplicate
and mark it as permitted before calling `#to_h`.

    params = ActionController::Parameters.new(name: 'Senjougahara Hitagi')
    params.to_h # => {}

    unsafe_params = params.dup.permit!
    unsafe_params.to_h # => {"name"=>"Senjougahara Hitagi"}

    safe_params = params.permit(:name)
    safe_params.to_h # => {"name"=>"Senjougahara Hitagi"}

This change is consider a stopgap as we cannot chage the code to stop
`ActionController::Parameters` to inherit from
`HashWithIndifferentAccess` in the next minor release.

Also, adding a CHANGELOG entry to mention that
`ActionController::Parameters` will not inheriting from
`HashWithIndifferentAccess` in the next major version.

Make sure :checkout_timeout and :dead_connection_timeout are numbers
Conflicts:
	activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

Remove to_s from reflection.type in add_constraints