Refactored TimeSeries object

- No longer a global configuration for 1993
- Moved cut-off functionality into a self-contained function with an
incoming param switch (default to true) whether or not to cut off date
to lower bound (1993 currently)
This function takes a startDate parameter, but it's not clear if you wanted this parameter to be used as an optional cutoff parameter, or if it's just there as a remnant of being a utility function.  Either way, this parameter is unused within the function and never provided by methods calling this function.