When the user clicks a structure and the Movies window is open, the Atlas
program must somehow find out what movies are appropriate to be played to
best illustrate that structure. This is done by searching a previously-loaded 
list of entries called a "movie map", which associates each structure with
one or more movies under appropriate titles.

The content of the files is a single two-level list containing the following:
((structure title movie-file) ... (structure title movie-file))

A specific example might be:
(("amygdala" "Dissections" "dissections.mov")
("amygdala" "Peel Surface" "surface.mov")
("amygdala" "Translucent Cortex" "cortex.mov"))

If this map were in use at a time when the user clicked a structure named
"amygdala", the Movies window would display a list of 3 titles: "Dissections",
"Peel Surface", and "Translucent Cortex".  The first of these would be
shown as the default movie in case the user just clicked the "PLAY" button.