Allow log level configuration via Jalview's Java Console, and a Copy to Clipboard button

Allow the user to select/change the log level being reported by Cache.log into the Java Console.

This is normally done by setting the logs.Jalview.level property in .jalview_properties (manual text edit) which becomes a permanent setting.

This addition will allow a user to easily set a DEBUG log level in the Java Console that is non-permanent, and a Copy to Clipboard button which will make it easy for the user to email log output.