New features

Initial DEV release.

A few improvements since Beta1, thanks to all contributors:

• Added group main for sample skin X: Testimonial to declutter other skins.
• #2759639: Remove @file tag docblock from all the .php files..

Yay! No bug reports since Beta2. Just a few refinements and descriptions.

A few fixes since Beta2, thanks to all contributors:
#2769485: Image styles not generating
#2765889: Loading icon is showing all time and setting display not working

A few small fixes and improvements since Beta2:

• Refined SlickMediaFormatter::buildMedia() to only accept slick_media plugin.
• Removed unused "nested_*" options.

A few fixes and improvements since Beta2, thanks to all contributors, even if not mentioned below: