espion: fix assigning GUI_VALUE_BOOL
Make property hardly dependent on op.

  There are two functions to add property now:
  - prop_create_empty_for_op()
    so need to add values with prop_value_append
  - prop_create_for_op() which creates property with values.

  We don't save property name anymore, because we have op name.

  Going to remove first one.
no more prop_value_append

  - need to think how handle _prop_new_value, which is outside of
 gui_widget
  - is it possible to remove prop_validate(), and validate value
  in gui_value_set()?