refs #4476

There is a problem in this patch, mostly noticeable in MP: When changing the values as a player, the values will first change by the GUI handling. Then at the next simUpdate (new turn), the values will move back to the old ones and a few turns later, the values will move back to what they should be (since the command is only executed a few turns later). This is obviously wrong. To counter this, we can add a if (g_Observer) check. Which would be correct in the sense that observers can't change the simstate, and should just view what the current sim values are. However I also considered #2459, if the values change otherwise than playerdoing, we will be in trouble. I presume fixing this there would need some event-based gui handling. We could argue this out of scope.

Some more history of the bug: The same issue was present when implementing the trade dialog in rP14417, however observers couldn't change perspective at that time. Then rP17675 fixed the issue partially, since it would only update the values on dialog open, and not while the dialog was open. rP23072 reverted to the original situation after rP14417, but kept the functionality that observers can change perspective.

Proper fixing indeed out of scope especially since more functions/buttons are probably affected.