Allow adding MemoryImage using URL

[ivanlanin]

The current version of PHPWord only allow dynamic image when the source string contains .php. When allow_url_open = on, the GD library functions that we use, e.g. imagecreatefromgif, can get images from URL.
Code sample:

$source = 'http://php.net/images/logos/php-med-trans-light.gif';
$section->addText("Remote image from: {$source}");
$section->addMemoryImage($source);

I've also done the following things:

1. Create 2 more samples from the old folder
2. Create unit test for PHPWord\Settings Add XMLWriter Compatibility option #119
3. Test & migrate the remaining old samples as per Mission to 0.7.1 #43

[Progi1984]

@ivanlanin Do I merge it ?

[ivanlanin]

Ok. Please merge. I've just finished testing footnotes. It turns out that MS Word cannot open the DOCX with footnotes that we created. OpenOffice doesn't have any problem. I fixed the bug.