[pt] [3.0] Update index.rst

Removed 2.x content and added current english documentation content.
[pt] [3.0] Update index.rst

Removed 2.x content and added current english documentation content.
Corrected a bad word reference.
Move getting help up higher.
Start moving files and content around for new intro.

The first part of the new toc will be a new intro/overview that shows
some quick code examples and overview information for CakePHP. I think
the destination TOC might not be possible, but we can get pretty close
through effective restructuring.
Merge old understanding doc into the overview.
Continue work on new intro chapter.

It is much more slim than the old one which was a bit verbose, pedantic,
and condescending in nature. I think we can add more of the explaination
into an improved tutorial, that I'll be working on soon.
Trim more fat.
Fix broken links.
Fix TOC depth.
Fix mistake.
Fix more mistakes.
Update url.rst
Merge pull request #1764 from mchiron/patch-1

Update url.rst
Fix mistakes.
Merge pull request #1757 from andtxr/patch-1

[pt] [3.0] Update index.rst
Pluralize fixture names
Pluralize ArticleFixture
Add event propagation example for behaviors.
indentation
Merge pull request #1767 from cakephp/3.0-behaviors

Add event propagation example for behaviors.