Update all planning problems to used const ScopedStates.

[Sherdil Niyaz]

We've now fixed all planning problems to hold ScopedState instead of raw state pointers. Unfortunately, we can't actually declare these ScopedStates to be const because of strange C++ typing issues.

This is a pretty minor issue (the fields are all protected anyway) but we should go back eventually and handle this.

See: #569