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.)
You can create a single xpath query for your two regexes btw by seperating them via | 
e.g. https://github.com/owncloud/news/blob/master/articleenhancer/xpathenhancers.json#L20