Alias *_pile -> pile_of_*

BUR #10097 has been approved by @nonamethanks.

create alias skull_pile -> pile_of_skulls
create alias corpse_pile -> pile_of_corpses
create alias trash_pile -> pile_of_trash

Making easier to find them + getting rid of redundant tags. I might revert one or more alias if necessary.

Not sure if book pile is also worth aliasing to pile of books.

Edit: fixed.

They should be using the singular form, like skull pile (which already exists btw).

The bulk update request #10097 (forum #211449) has been approved by @nonamethanks.