[CHANGE] In settings.py, DATABASE_DIALECT was changed to postgresql

[FIX] In actions.py, insert function doesn't drop ttable anymore
[CREATE] In database_table.py, DatabaseTablePsql was created
[FIX] In database_table.py, apply_derivatives DatabaseTable method has now a conditional to verify self._derivatives lengh
[UPDATE] In database_table.py, gen_data_table function has a conditional to verify the dialect