"Hide robots" shortcut should not hide visible system robots

[byorgey]

Describe the bug
Hitting Alt-h to hide all robots for a few seconds also hides system robots, e.g. growing seeds. The fact that growing seeds are robots is an implementation detail the player should not know or care about.

To Reproduce
Start the tutorial Farming scenario, harvest a tree, then hit Alt-h and observe the growing tree seed disappear temporarily.

Expected behavior
Hiding robots should only apply to robots created by the player.

Additional context
I am not sure whether system robots should be hidden when in creative mode. In a sense, even when in creative mode it still "breaks the fourth wall" for the player to learn that growing seeds are implemented as robots. One might imagine a separate "debug mode" in which hiding does apply to system robots.