spice-display: Move auto-clipboard to 'General' section

Designers (jimmac and aday) want to ditch the 'Display' section, so we
need to move this to 'General' section, which is more appropriate for it
anyway.
remote-machine: Move 'Protocol' to 'General' section

Designers (jimmac and aday) want to ditch the 'Display' section, so we
need to move this to 'General' section before we do that.
vnc-display: Move 'Read-only' to 'General' section

Designers (jimmac and aday) want to ditch the 'Display' section, so we
need to move this to 'General' section before we do that.
properties: Drop 'Display' section

This is based on input from our designers (jimmac and aday). Now that we
have removed and moved all options under this section, we can simply
ditch it now.