kstyle: Port memory management to C++ stdlib pointers

This is done for consistency and increased memory safety. Use shared_ptr for the shared Helper, and unique_ptr for the rest. Add default argument for parent in constructors, and actually don't pass parent at all because automatic lifetimes does play well together with QObject parent/child based lifetime management.

Remove worthless comments like these, and just use smart pointers:

    //* window manager
    WindowManager *_windowManager = nullptr;