All the previews (in Mail, Contacts, Memos and Tasks) stop using
deprecated WebKitGTK+ DOM API through a WebExtension (and its D-Bus
API) and start using the JavaScriptCore API (and JavaScript as such).
This allows to lightweight the WebExtension for the EWebView
significantly, including drop of the D-Bus API of it, fully relying
on the Inter-Process-Communication of WebKitGTK+ itself.
