Drop role management

Roles are not created anymore, previously private functions for table
information extraction (CDB_UserTables, CDB_TableIndexes, CDB_ColumnNames,
CDB_ColumnType) will now be callable by anyone while only returning
information about tables over which the calling user has SELECT privilege.

Closes #36

scripts-available/CDB_ColumnNames.sql

@@ -11,6 +11,3 @@ AS $$
          
 $$ LANGUAGE SQL;
 
--- This is a private function, so only the db owner need privileges
-REVOKE ALL ON FUNCTION CDB_ColumnNames(REGCLASS) FROM PUBLIC;
-GRANT EXECUTE ON FUNCTION CDB_ColumnNames(REGCLASS) TO ":DATABASE_USERNAME";