Corrected how the existing and reduction datetimes are compared.
CommonJS require is not supported in reduce functions. Copied lmsutils.DateFromISOString and lmsutils.DateToISOString into d2l_user's reduce function for now. Will modify the map function in the future to emit straight integers instead of ISO 8601 dates in the future to eliminate this.
Merge branch 'master' of https://github.com/ucalgary/ps-lms-batch-extract