React 16.8+ Compatibility

Semiotic 2.0 deprecates a lot of old compatibility props, removes the download button and gets rid of deprecated lifecycle events. It should also (hopefully) take advantage of some of the newer React features. Please take a look and file any issues you discover.

• DownloadButton is gone. It provided some convenience and much hassle and my philosophy on how to handle exporting data is that it should be a case-by-case feature handled outside of the dataviz framework.
• Since everyone didn't always want to render with sketchy rendering it's optional now, so to enable sketchy rendering you will need to import Rough or a Rough-like library and pass it to your frame using the sketchyRenderingEngine prop. So something like:

import roughjs from "roughjs/dist/rough.es5.umd.js"
<XYFrame 
   sketchyRenderingEngine={roughjs}
/>

• Old names for props (like areas in XYFrame which was replaced by summaries) are no longer honored.
• react15Wrapper is removed from FacetController since React 15 is no longer supported
• wordcloud has been removed from NetworkFrame it was never a very good word cloud

Other changes should be coming. If you have any suggestions just let me know. Bugfixes to 1.X will, of course, continue.