[fix] google images engine: Fix 'scrap_img_by_id' function

The 'scrap_img_by_id' function didn't return any longer anything useful.  This
fix allows the google images engine to present the full source image instead of
only the thumbnail.

The function scrap_img_by_id() is rpelaced by a fully rewrite to parse image
URLs by a regular expression. The new function parse_urls_img_from_js(dom)
returns a mapping of data-id to image URL.

Closes: https://github.com/searxng/searxng/issues/909


Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>