WebPage thumbnails

Setup the ability for webpages to be accessed as thumbnails. There are
also Restriction levels that can be set by the json file; either page or
domain restriction. Currently the screenshot capture isn't working
right; so the thumbnails are blank.

In another test I noticed that PDFs were rendering in the QWebView, so
migrating from MuPDF to QWebview will be next IF I can get the plugin
iframe to stop popping out.
Merge branch 'master' of https://github.com/TheGadgetCat/CORAL