Support C++ private: class members with getter() functions

[KeyWorksRW]

Description:

Ideally, a Base class should have private: rather than protected: class members, with a protected or even public function used as an accessor. This is particularly true for generated classes where the class members are normally pointers that a derived class can get() but should not set().

Right now there isn't any way to do this because there is no private: option in the class access drop-down list. There is a way for a dev to add their own getter function, but without the private: option, it's useless as a getter function.

Design change

1. Add private: to the drop-down list. Note that this isn't required for non-derived classes which have the option of converting all protected: members to `private:' but it would avoid potential confusion.
2. Add a getter() function below the class access that is disabled unless class access is set to private:'. The getter() function would be added as a protected:` function. Note that we would need to verify uniqueness of the function name across the entire form, including any class methods the dev may have added to the form.