Allow to use javascript properties in sao
Javascript allows for python like properties: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects#Defining_getters_and_setters
This feature is supported by all major browsers: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/get#Browser_compatibility
Sao's inheritance mechanism (Sao.class_) is not compatible with those, yet it requires a simple patch to do so.