Merge topic 'python-numpy-integration'

c5330ac7 python: if lib not available skip custom loader
ebc35aea python: flush dependency only after initial import request complete
1f6067bf python: raise ImportError instead of RuntimeError
446dae5a python: defer import of dependencies after native lib init
d3e3b1eb python points can be set from vtkPoints or numpy array
51d11b0f python pickle registration with override
00d5cb9d python: call decref on method call result
d6881928 python: code cleanup on module loading
...

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !11522