* ui/conversation-message.ui: Split out preview labels from existing
header box and create a new preview box for them.
* src/client/components/main-window.vala (MainWindow::set_styling): Use
style-defined names to allow us to specify message row backgrounds better.
* src/client/conversation-viewer/conversation-message.vala
(ConversationMessage): Update GTK composite template children
properties and visible state when showing/hiding the body, set new
preview/header box label texts.
* src/client/conversation-viewer/conversation-viewer.vala
(ConversationViewer::do_embedded_composer,
ConversationViewer::add_message): Don't add 'frame' class to conversation
list rows, we're styling it explicitly now.
d0dc003772