Move constructor and move assignment operator have to be defaulted or
deleted to follow the rule of five. ScopedDialog is supposed to live
inside a specific scope, so moving it doesn't make sense. A similar
class template QScopedPointer is also not movable. So let us define the
move operations as deleted via Q_DISABLE_COPY_MOVE.

Unlike Q_DISABLE_COPY, Q_DISABLE_COPY_MOVE prevents the forwarding
constructor from acting as a move constructor. So the following code
    ScopedDialog<QDialog> s;
    ScopedDialog<QDialog> s2(std::move(s));
compiled before, but does not compile at this commit.

Move this declaration closer to other special member functions.