Make GObjectIntrospection classes and methods writable
Make GObjectIntrospection classes and methods writable

Modify the default JSPROPERTY flags to remove JSPROP_READONLY, so
it is possible to replace the methods and classes from overrides.

https://bugzilla.gnome.org/show_bug.cgi?id=646633

djdeath/gjs,magcius/gjs,djdeath/gjs,magcius/gjs,mtwebster/cjs,djdeath/gjs,pixunil/cjs,endlessm/gjs,pixunil/cjs,magcius/gjs,pixunil/cjs,endlessm/gjs,mtwebster/cjs,mtwebster/cjs,endlessm/gjs,pixunil/cjs,djdeath/gjs,endlessm/gjs,magcius/gjs,djdeath/gjs,mtwebster/cjs,mtwebster/cjs,endlessm/gjs,pixunil/cjs,magcius/gjs