Blender Git Loki

Point users to new location of "Show Group Colors" option

In ad85256e7108 the "Show Group Colors" option was changed from a
per-editor option to a user preference. Since so many people wanted to
turn this option off, this makes sense. However, this move caused some
confusion because the option was just gone from the menu.

This commit adds a dummy menu item. It's disabled, and the tooltip
explains that the option can now be found in Preferences.

T83390 was created to track the removal of these hints.

Reviewed by: Severin

Differential Revision: https://developer.blender.org/D9735