Add filters for selecting members to add to Python as done in QLua

[candycode]

When an object or type is added to the Python context do allow client code to select which methods and properties are actually added through a filter object or RegExp.

Pass an additional MemeberFilter object to the context which is used to filter members.

E.g.

struct MemberFilter {
    bool MethodAvailable(QObject* obj, const QMetaMethod& mm) const = 0;
    bool PropertyAvailable(QObject* obj, const QMetaProperty& mp) const = 0;
};