Update SlideshowSkin to ViewsSlideshowSkin + update theme preprocess to use new Skin mechanism

[vbouchet31]

There is an issue in .theme.inc as

$skin = $skinManager->createInstance($options['slideshow_skin']);

throw an exception due to a missing class.

“Plugin (default) instance class “Drupal\views_slideshow\Plugin\SlideshowSkin\DefaultSkin” does not exist.”

[vbouchet31]

Fixed: Mistake in namespace definiton. (facepalm)

To reproduce the issue:

• Enable Views Slideshow and Views Slidehsow Cycle
• Download http://malsup.github.io/jquery.cycle.all.js and place it /libraries/jquery.cycle/
• Create a new View
• In "Format", use "Slideshow"
• Click the "Settings" link aside the selected format
• As there is only one "Skin" and one "Type" (i.e "Cycle"), you only need to save the form, save the Views and visit the page showing the Views (or place the block).
• A skin is simply a class to be added to the render array and potentially some libraries.

In views_slideshow.theme.inc, _views_slideshow_preprocess_views_view_slideshow() is the function defined by the Views style plugin to render it. Around the line 100, we try to access the skin attribute by using ->getClass() and ->getLibraries().

$skinManager = \Drupal::service('plugin.manager.views_slideshow.slideshow_skin');
$skin = $skinManager->createInstance($options['slideshow_skin']);

get a blank page with

An error occured, blablabla and throw in logs Drupal\Component\Plugin\Exception\PluginException: Plugin (default) instance class "Drupal\views_slideshow\Plugin\ViewsSlideshowSkin\DefaultSkin" does not exist. in Drupal\Component\Plugin\Factory\DefaultFactory::getPluginClass() (line 87 of /Users/vincent.bouchet/Sites/devdesktop/d8b14/core/lib/Drupal/Component/Plugin/Factory/DefaultFactory.php).

If I try to use the getDefintion:

$skinManager = \Drupal::service('plugin.manager.views_slideshow.slideshow_skin');
$skin = $skinManager->getDefinition($options['slideshow_skin']);
dsm($skin->getClass());

get a blank page with

Fatal error: Call to a member function getClass() on a non-object in /Users/vincent.bouchet/Sites/devdesktop/d8b14/modules/contrib/views_slideshow/views_slideshow.theme.inc on line 102