See lengthy discussion at https://code.wildfiregames.com/rP22266
This patch does the following:
* move `territory_pull.xml` out of `special/` to make it placeable
* insert <Visibility> node to solve Atlas errors
* convert it into a generic template (`template_pull.xml`) with a related `pulls/` subdirectory for its children
* created six territory pull children (each with a Weight : Radius ratio of 1000 : 1)
* only one is used, in `maps/scenarios/Campaign Test Map.xml`, but the others might become useful when people start making campaigns in the future
* created six vision pull children
* unused now, but could be quite useful for scenarios (to temporarily grant vision around a point)