Default text selection on popular sites

When there is no text selected, the extension could select a default text based on the current domain and a given XPath set in the extension. For instance on http://www.bbc.com/news/world-europe-26465962, the news text could be selected automatically. And on Wikipedia, the article text.

Start by examining the extension's current text-selection handling and how domain-specific settings or XPath values are represented. Reproduce the no-selection behavior on the BBC and Wikipedia examples, then define completion as selecting the configured article text automatically for supported domains without overriding an existing selection.

Written by the indexing model from the issue text.