chatview: change visibility of reply component

Make it so that the reply/more/share buttons are visible
whenever the cursor hovers over the horizontal area
that a message takes up. Add message highlighting.
Fix small issue with "more" button not being deselected
after choosing an emoji

GitLab: #1870

Change-Id: I4db5230c2a50ce4640eececc69f8e88348356d79