Refined spiegel.de enhancer and added androidpolice.com

This patch adds an androidpolice.com xpathenhancer and refines the existing spiegel.de xpathenhancer. (Remove empty bullet points from top of article and add author credit at the bottom.)
I think rather than using a regex we should use xpath, see https://github.com/owncloud/news/blob/master/articleenhancer/globalarticleenhancer.php#L35 how to do this without running into XXE issues