This adds complete move and noexcept semantics to vtkNew, vtkWeakPointer,
and vtkSharedPointer, while doing more robust type-checking. In
particular, this patch may expose bugs of the form:

vtkWeakPointer<vtkRenderer> ren = ...;
vtkWeakPointer<vtkCamera> cam = ...;
cam = ren; // Shouldn't compile: types are unrelated.

since vtkWeakPointer can no longer be constructed from an arbitrary
vtkWeakPointerBase.

Similarly, the comparisons between these objects has been updated.
Comparing unrelated pointers is illegal in C++, and code such as:

vtkSmartPointer<vtkIntArray> array1 = ...;
vtkSmartPointer<vtkFloatArray> array2 = ...;
if (array1 == array2) { ... }

no longer compiles (similar to comparing float* and int*).

All move operations are made noexcept to allow optimizations when stored
in std containers (e.g. std::vector reallocs will now move instead of
copy, bypassing reference counting).

Note that some move operations (eg. move-constructing vtkWeakPointer from
vtkNew, or move-assigning to a vtkSmartPointer) are not implemented, as
they either don't makes sense, or don't provide any advantage over copying.

vtkWeakPointer has been updated to treat vtkNew<T> like T* when
constructing or assigning, similar to vtkSmartPointer.

The enable_if statements have been replaced with static_asserts, since
these will give nicer error messages ("Pointee types are incompatible",
rather than "no matching overload found").