README: Add information about the fork
Remove releases files
Remove demopage
Remove build stuff
Remove jquery lib
Merge branch 'master' into dev
Make `.lb-nav` element cached
Refactor image loading

Add possibility to add more image types.

Use `_imageLoader` map to get a proper loader function. Move "fit image"
related code to a separate function `_fitImage`.
Add experimental support of Youtube embedded videos
Add classes to previews and container depending on the image type

Also add a sample style to "youtube" images.