Initial feature for starting: `bps_list_*` functions family

[akherlan]

• writing user interface functions bps_list_domain() , bps_list_subject(), bps_list_table()
• writing builder functions for utilities in R/utils.R
• writing variable functions (need suggestion for the best way to store variables) in R/variables.R
• default token is supplied from Sys.getenv()
• update contributors