New feature: Added "Newsletter Subscription Form" widget

[empiricompany]

Description (*)

Add a new widget with newsletter subscription form.
It is useful for me to be able to insert the newsletter subscription form into CMS pages or Static Blocks.
I have always manually inserted this piece of code:
{{block type="newsletter/subscribe" template="newsletter/subscribe.phtml"}}

With the widget become:
{{widget type="newsletter/widget_subscribe" template="newsletter/subscribe.phtml"}}

But is the same, if you look the new block widget subscribe only extend block subscribe

class Mage_Newsletter_Block_Widget_Subscribe extends Mage_Newsletter_Block_Subscribe implements Mage_Widget_Block_Interface

Manual testing scenarios (*)

1. Insert Newsletter Subscribe Form Widget
2. Test with cache if form_key correctly change

Questions or comments

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• Add yourself to contributors list

[addison74]

This is a good idea. Maybe we can extend it into another PR to the contact form too. But this would a little bit complex.

[fballiano]

I would prefer not having the constructor only calling parent constructor, but I'll merge it anyway in a couple of days if we don't get more feedback

[empiricompany]

I would prefer not having the constructor only calling parent constructor, but I'll merge it anyway in a couple of days if we don't get more feedback

I can remove it it's not a problem

[addison74]

I tested the PR. It adds to the list the newsletter widget that I used it on a CMS page. In the Frontend the form is displayed as expected and I successfully subscribed.

[addison74]

@elidrissidev, @kiatng - please stamp this PR with your green color.