Adds a parsing step when constructing `Message` objects that scans the
message content for anything that looks URL-like, and inserts new
`TextChunk`s into the message content with a URIPayload set.
Hovering over a URL shows an on-hover effect. Clicking a URL opens it in
the default browser. Right clicking shows the hostname, with an option
to open and an option to copy the URL to the clipboard.
Dean Sheather
Anna