Use area instead of location or room

Since the term "location" was already used for the name of the facet
identifying the area where an element is located, it was vague to also
use that term for a class of elements which serve as those locations.
Instead use the term "area" since it's as descriptive and shorter. Also
avoid the term "room" as a synonym since areas can be outside as well as
indoors. This further implies renaming the location.mpy sample file to
become area.mpy instead.