#853 Make wxParentProperty read only in wxsChart (r11783 appendix)

[Miguel Gimenez]

Moved from the forum, http://forums.codeblocks.org/index.php/topic,23361.0.html

Commit 11783 fixed a build error with wxWidgets head changing wxPGProperty to wxStringProperty. This property shouldn't be modified, so it was made read only in wxsstatusbar.cpp.

Later, user sodev reported that wxschart also used this property, so it needs to be made read only also.

This patch makes the property read only. It also simplifies the code using the macro NEW_IN_WXPG14X defined in property.h.