fixed: getters method (Model::*getter_method)(pt::Stream &) produced boolean value when serializing to flat string

- changed in Model::field_list_generic(...): message "you should set FT::is_foreign_key or FT::is_foreign_key_in_child flag" print only
  for work mode MORM_MODEL_WORK_MODE_SET_PARENT_ID or MORM_MODEL_WORK_MODE_ITERATE_THROUGH_CHILDS_WITHOUT_FOREIGN_KEY
- pt::TextStream::to_string(...) is now pt::TextStream::to_str(...)
- in Model::get_raw_value() for ezc 'pt::TextStream & stream' changed to 'pt::Stream & stream' (a base class of pt::TextStream)
  similar in field(...) methods which take getters: void (Model::*getter_method)(pt::TextStream &) -> void (Model::*getter_method)(pt::Stream &)

src/dbconnector.cpp

@@ -110,7 +110,7 @@ bool DbConnector::query(const char * query_str)
 bool DbConnector::query(const pt::TextStream & stream, QueryResult & query_result)
 {
 	std::string query_str;
-	stream.to_string(query_str);
+	stream.to_str(query_str);
 
 	return query(query_str, query_result);
 }