This makes it easier for modders to use different template organization schemes.
(Other folders, more folders, different names, etc.)
This considers only templates starting with template_ or special/ to be unplaceable,
if you want more unplaceable templates start the name with template_ (in the root
template dir), or put them in special/ or a subfolder thereof.
This makes rubble/ placeable, as the only thing placing one of those does is
making them disappear very soon, so might not be quite what a user expected,
but that doesn't sound like a very good reason to prevent them from placing them.
Might be usable for a story map where the player starts in an area where things
were destroyed recently, but shouldn't stay around forever.
This also makes other/catafalque placeable. This previously was not placeable
due to a limitation of the related trigger script, and the underspecified interaction
with the number parameter in the gamesetup. See #4762.
Alternate proposal to D878.