LP1823367 Move away from "volume" moniker internally

LP1823367 Move away from "volume" moniker internally

It isn't really correct to use "volume" and "call number"
interchangeably.  This code substitutes various forms of the second
for various forms of the first within the internal variable and
function names.  To help contain the change, it tries to only do so
for values which are native to eg2, and not leaking from or into other
interfaces.

Understanding that this change is somewhat disruptive, I still think it
is in our overall best interest, as it will help us from falling into
old habits, and it will help future coders better understand the
relationship between the code and the interface.

Note, this code does not change any filenames.  This is for review
purposes to allow the changes to be more easily observed.  If accepted,
we should change couple of affected filenames as well.

Signed-off-by: Dan Wells <dbw2@calvin.edu>