Added ui.button as dependency of ui.dialog

While developing my own module, i've upgraded installation to latest version of PS and impacted a bug:

$('#something').dialog({...}); caused an error: t().button is not a function.



In my php code i had this:
$this->context->controller->addJqueryUI('ui.dialog');

i found that it doesn't load ui.button dependency.

Added 'ui.button' to classes/Media.php at the end of ui.dialog dependencies and all worked fine.
Merge pull request #720 from makk1ntosh/development

//Added ui.button as dependency of ui.dialog