Add a command line option to set Jalview properties for this session only

java has -Dpropertyname=value

gradle has -Ppropertyname=value

jalview should have --Ppropertyname=value
specifically for Cache properties.

These should only persist for the current session, and not affect the applicationProperties or storage thereof. They also shouldn't affect the values displayed in the Preferences pane (otherwise when it comes to saving some other changed preference the session property will overwrite the stored property).

If a Preference is changed, it should delete the session property and use the new changed property.