Adding Group support for PowerPoint2007.

[joshuadoss]

Changes include:

1. Adding the ability to group shapes together on a slide.
2. Adds (or corrects, depending on perspective) extent and offset calculation on slides.
3. Unit test for new Group object.
4. New sample (09) to generate PowerPoint with grouped objects.
5. Change to CHANGELOG.md.

[Progi1984]

Hi @pr0phet, could you :

• fix your PHPCS errors : https://travis-ci.org/PHPOffice/PHPPowerPoint/jobs/42919909#L297 ?
• fix this PHPUnit failed test : https://travis-ci.org/PHPOffice/PHPPowerPoint/jobs/42919909#L320 ?
• may be add the support for ODP writer ?

Thanks for this great PR.

[joshuadoss]

Thanks @Progi1984. ODP will take a few days.

[Progi1984]

@pr0phet No, Thanks to you for this big PR. I will wait for your ODT improvement.

[joshuadoss]

@Progi1984 I think I hit the same issue that you hit a few months back. That's the only thing that I can see is wrong with the PHP 5.3.3 build of the code. I tried to see what you did to fix your issue in Chart.php, but it appears you didn't do anything to the code to make the issue go away... Any input would be appreciated.

[Progi1984]

@pr0phet Could you pull the last version of the develop branch and commit it ? I could merge this one after.