Menu-type actions were restricted to rendering in the order that actions

were registered, but this is highly annoying when pulling in actions

from multiple different places, including extensions.
This change adds the ability for a menu action to define the order of

the children, and adds a new separator implementation (defined with the

custom "--" name in the order). Any actions which are in the menu but

not explicitly specified in the child order will be added at the end of

the menu.

Created a menu action and specified the child order. Saw that I was able

to reorder the menu items as expected. Verified that separators worked

and looked good.