Wrap more device pointers in DeviceBuffer

Wrap more device pointers in DeviceBuffer

Store and pass around more device pointers as DeviceBuffer<T>
instead of as a raw or even void pointer.

Related changes:

- PmeGpu->kernelParams->atoms.d_forces is now RVec, not float. Forces in
  most other places are RVec, so it seems more logical.
- GpuForceReduction::Impl::baseForce_ now stores pointer to the
  beginning of the array, without shift.