Copy/Paste from system clipboard uses Control key instead of Command key
On macOS, the command for copy and paste is Command+C and Command+V respectively. However, OpenMW instead has this mapped to Control+C and Control+V, as it is on Windows and Linux.
OpenMW already uses proper key commands for other functions, such as quitting the app (Command+Q), so it ought to also support the proper commands for copy and paste.
(RM-3934 from redmine: created on 2017-06-26 by Will Herrmann, , closed on 2017-08-11 by Will Herrmann, relates #4023)