Webkit shared process redux
This re-instates the changes made in !374 (merged) to re-use a single WebProcess instance for displaying email, but also converts client/JS communication using WebKitGTK's new UserMessage
API to fix JS to client communication that was broken by moving to a single process model (see https://bugs.webkit.org/show_bug.cgi?id=204839).
This looks like it may help with #283 (closed) but introduces some other issues with quote expanding/collapsing.
Edited by Michael Gratton