Support lazy loading images

[nikolay-borzov]

See https://github.com/nikolay-borzov/user-scripts/issues/71 for background

A user-script disabling lazy loading

• List of possible lazy load attributes:

_src
data-actualsrc
data-cover
data-defer-src
data-imageurl
data-ks-lazyload
data-ks-lazyload-custom
data-lazy
data-lazy-load-src
data-lazy-src
data-lazyload
data-lazyload-src
data-original
data-placeholder
data-src
data-thumb
data-thumb_url
data-url
file
imgsrc
load-src
origin-src
original
real_src
src2
zoomfile