Teach MetaHelper::meta() to accept array from 'Meta' configure key.

Allows:

	Configure::write('Meta', array(
		'author' => 'rchavik',
		array('attribute' => 'og:author', 'content' => 'rchavik'),
		array('http-equiv' => 'refresh', 'content' => '5'),
	));

To generate:

	<meta name="author" content="rchavik">
	<meta attribute="og:author" content="rchavik">
	<meta http-equiv="refresh" content="5">
Extensions: Parse composer.json in plugins dir

Closes #339
Extensions: Teach reading composer.json with croogo-theme type
Fix: When screenshot info is missing, show an empty column
Merge branch '2.0-composer.json' into 2.0