refactor the way oodml find-all and select deal with their keyword args.

refactor the way oodml find-all and select deal with their keyword args.

 * introduce filter-plist for filtering key-value pairs out of a plist.
 * switch some (apply #'some-fun (append args (list :key val)))
            to (apply #'some-fun :key val args)
       where we know the key isn't in the args list