ContentExtractor: refactor extractEntity
ContentExtractor: refactor extractEntity

extractEntity has been renamed extractEntityFromQuery and takes a XPath
expression instead of CSS class. It takes an optional callback for the
return value and it silents exceptions occuring during node deletion.

Signed-off-by: Kevin Decherf <ffb4761cba839470133bee36aeb139f58d7dbaa9@kdecherf.com>

j0k3r/graby,aaa2000/graby