Improve js written for guides

* Stop using unnecessary global variable
* Use function defined by jQuery for simplicity
* Fix event listner for "more info button" to handle
  event on resize browser
Add few information about missing steps [ci skip]

Add some deprecations previously note covered such as the confirm
option for the link_to helper or options which aren't needed anymore

Also add a mention about the config.assets.js_compressor option.
Document where `column` param gets utilized in `substitute_at`.
Add CHANGELOG entry for #11348
Use helper method to get ENV['CONTENT_LENGTH']
Use Request#raw_post instead Request#body

In order to get raw_post to be not empty after
ParamsParser#parse_formatted_parameters,
added rewinding of body stream input on parsing json params.

Closes #11345
cache.exists? should return true/false
Explicitly test for true and false.
Creating a class for carrying out rails commands.

This class encapsulates a lot of logic that wasn't very object oriented.
Helper methods have been created to try to make things more logical and
easy to read.
Update 'Active Record Migrations' guide [ci skip]

Delete an unneeded line.
params keys are Strings
1.9 Hash Syntax
Fix SyntaxError in guides sample code

[ci skip]
Merge pull request #11359 from willnet/patch-1

Update 'Active Record Migrations' guide [ci skip]
Added cursor pointer for 'More Ruby on Rails'

dropdown menu on guides page (which appear on small windows)
[ci skip]
Fix 2 grammatical errors/typos in Active Record Basics guide. [ci skip]
Merge pull request #11363 from dpdawson/master

Fix 2 grammatical errors/typos in Active Record Basics guide. [ci skip]
handle notes in *.sass files
Merge pull request #11367 from artemeff/sass_in_notes

handle notes in *.sass files
Merge pull request #11355 from wangjohn/class_for_rails_commands

Creating a class for carrying out rails commands.