Feature: ability to re-order user build templates

[lL1l1]

Describe the feature
"Be able to re-order hotkey cycling of templates without having to re-create them all in the desired order." (Arran on the forum)

Expected behavior
Be able to drag user templates around

like you can drag units in the factory queue:

and then it should update the order in which they appear when using the "cycle user templates" hotkey.
I think the place to start looking is in build_templates.lua. The current issue is that the hotkey relies entirely on the order of templates in the game.prefs file/table.

This should also apply to factory build queue templates.