update Wikipedia plugin to generate HTML, and other improvements

[titaniumbones]

At present, Wikipedia plugin grabs plain text from Wikipedia pages by stripping HTML tag regexes from the HTML provided by the API. Unfortunately, the first several paragraphs of many pages include a lot of text that is hard to interpret without those tags. it would be better to

• identify selectors of generally unwanted page components, and strip those from the API response. This should include at minimum redirect notices, section edit links, TOC elements, summary tables, and perhaps all images & captions.
• rewrite relative links as absolute links, so they can be properly clicked.
• consider adding a default target or onbeforeunload event handler to reduce unwanted navigation away from page.
• replace numberofwords with numberofparagraphs paragraphs
• currently all wiki plugins live inside the same div. Is that the right decision? Shouldn't each one have its own context? Add a wrapper around each instance, simplifying the code a bit.