Images lazy loading: request WebP thumbnails
Use $wgEnableWebPThumbnails global
ImageLazyLoad: improve WebP support detection

* use AMD
* adding JS logging
* report WebP support stats to Kibana
ImgLzy: introduce wgEnableWebPSupportStats global
Handle wgEnableWebPSupportStats + JS linting
transition-shorthand: remove deprecated -moz-transition property
Merge pull request #3199 from Wikia/imglzy-webp-support

Images lazy loading: request WebP thumbnails