Show first wikipedia paragraph as teaser
Factor out (and fix) proxy URL creation
Use only the first sentence of the article as teaser
Improve teaser extraction

* Skip paragraphs that contain invisible spans, because they
are probably templates.
* Accept paragraphs/sentences without an ending period.
Improve sentence detection

* Check if the period is followed by a space or at the end of the text
* Continue if the period ends an ignored sequence like "e.V." or "bzw."