Fix Megalith's GetCommandQueue not functioning as expected

[lL1l1]

Issue

When checking the Megalith's UserUnit:GetCommandQueue, it would return its default factory rally point instead of its own move orders.

Description of the proposed changes

• Remove the FACTORY category that causes this behavior.
  • This required an adjustment to fix hotbuild's building functionality due to how it filters builders and factories. I explored an alternative with defining the CONSTRUCTION category as units that can start builds of other units but it would be incompatible with mods.
• Annotate some related categories' engine functionality.

Testing done on the proposed changes

Used the following command to confirm that units with the `FACTORY` category have this behavior.

UI_Lua 
local count = 0
local units = {}
for i,v in __blueprints do
	if type(i) == 'number' or string.find(i, '/') then continue end
	if v.CategoriesHash["MOBILE"] and not v.CategoriesHash["INSIGNIFICANTUNIT"] then
		units[count + 1] = CreateUnitAtMouse(i, GetFocusArmy()-1, math.mod(count, 17)*9, math.floor(count/17)*9, 0)
		count = count + 1
	end
end
ForkThread(function()
	WaitTicks(20)
	units = UISelectionByCategory('ALLUNITS', false, false, false, false)
	for _, unit in GetSelectedUnits() do
		local queue = unit:GetCommandQueue()
		if not table.empty(queue) then
			LOG('this unit has commands for no reason', unit:GetBlueprint().BlueprintId, repr(queue))
		end
	end
	IssueCommand('UNITCOMMAND_DestroySelf')
end)

Made sure that hotbuild issues the correct order so that Megalith can build a blueprint on the ground instead of building like a factory.

Additional Context

I noticed the Fatboy has the CONSTRUCTION category, but aircraft carriers do not, so Fatboy is a bit out of place for mobile factories.

Checklist

• Changes are annotated, including comments where useful
• Changes are documented in the changelog for the next game version