add mediators for Game Object Containers

[gnunua]

Description

• add mediators for Phaser.GameObject.Container
• example app update
• update tests

Related Issue

Here is the related issue #54

Motivation and Context

Managing all views directly form the scene mediators is complex.

How Has This Been Tested?

Testing withe example app

Types of changes

• Updated docs / Refactor code / Added a tests case (non-breaking change)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation. ( has been updated changedlog and readme)
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[saqsun]

nice!

[tiagoschenkel]

Nice contribution @gnunua!

I added some suggestions to the Changelog that can be covered in future pull requests.

Closes #54.