Move config.filter_parameters to you own initializer file

This is very rarely changed and does not deserve to be in application.rb
Fix documentation to content_tag_for [ci skip]
Update some code examples on the "Working with JavaScript in Rails" guide.
Merge pull request #8771 from lucasmazza/unobtrusive-javascript-examples

New code examples on "Working with JavaScript in Rails" guide.
Remove the content_tag_for change from CHANGELOG since it was reverted