[REQUEST] More tools in Python

### Is your feature request related to a problem? Please describe.
Since the current Python module only implements basic manipulation of grids, it would be very useful to have more access to tools such as `GridTransfomer`, `GridSampler`, etc.

### Describe the solution you'd like
Since templated classes are a bit more tricky to wrap in Boost.Python, an example of how this is done with one of these tools would help implement others.

Start by reviewing the current Python module and its existing Boost.Python wrappers, then compare how one templated tool is exposed. Use a tool such as GridTransformer or GridSampler as the example and identify the interfaces that need wrapping. Done means the requested OpenVDB tools are accessible from Python with suitable coverage.

Written by the indexing model from the issue text.