Add export/import to allow vtkTuple subclasses in other modules.

The python-wrapped vtkVector type wasn't able to link to its
python-wrapped vtkTuple superclass because vtkTuple was in a different
module.  This patch adds import/export declarations to allow module
boundaries to be crossed.

The trick of automatically discovering what template instantiations
are used does not work across module boundaries, however, so the needed
instantiations of the vtkTuple template have been hard-coded for now.

Change-Id: Ibeee7d3edcdfab491ad4c1907498a02f84dc86ed
Merge topic 'python-import-export' into master

c2bd3fdb Add export/import to allow vtkTuple subclasses in other modules.