* "name" and "param_name" is strongly connected with plugin's code (even in base classes)
   so these MUST be not changed by subclasses (subclass MUST use same names)
 * separate "param_name" from "name" to detect overwriting "param_name" by subclasses to raise errors
   and add "variable_name" method as internal utility
 * make it possible to change default values in finalized sections
   because it's very popular that 3rd party plugin prefer different default value for built-in predefined parameters
 * make it possible to change "init" specification of finalized sections
   because newly added/changed default values might be able to init sections

… style plugin

…ue in default)