Finished LM algorithm Python driver code

Things finished:

* Re-distribution of data for computation

* Finished the function to solve for the initial time series values

* Lots of comments that explain the contents of the intermediate tables
  that are used or generated by the SQL functions to be implemented

* Finished LM algorithm Python driver code. The framework of LM
  algorithm is done. We just need to implement the following SQL
  functions and C++ functions needed by them.

Things left:

* Implement the aggregate __arima_lm_agg SQL function for computing
  J^T*J, J^T*Z, Z^2 for each group

* Implement the aggregate __arima_lm_result_agg SQL function for
  accumulating the above quantities over all groups to get the
  J^T*J, J^T*Z, Z^2 for all data

* Implement the UDF __arima_lm_delta for computing delta

* Figure out how to compute likelihood, standard errors

* Implement the code for likelihood and standard errors