Create t_estimation_period and t_panel_refyearset_group tables
Motivation:
- estimation period is now assigned for each estimate in table t_total_estimate_conf by stating estimate_date_begin and estimate_date_end, this period is not so variable for the vast majority of estimates so the situation indicates usage of foreign key to same table where the period can be also somehow labeled
- the same situation occurs in panels and refyearsets combinations in tables t_panel2total_2ndph_estimate_conf
Solution:
- create table t_estimation_period and create foreign key from t_total_estimate_conf pointing to this table
- same applied on the t_panel_refyearset_group - at least foreign key from t_total_estimate_conf, maybe redirect FKEY from t_panel2total_2ndph_estimate_conf