[PR] List multymask conceptual SNL

[nortikin]

We have not node dealing with masking multiple lists

i.e. i have some obejcts that have different materials indices, i need to calc areas. i need sort pols [p,p,p,p,p,p,p] by materials with mask as [1,2,3,4,5,6,0] if i use list item, it gives indices, but not grouping pols to materials.

SNL multymasking

My commit https://github.com/nortikin/sverchok/commit/8afad585749f25f5149a7ac6b3c6a69fbbcb707e is all about this future node. Interesting, that keys for masking can be strings and other types.

[nortikin]

weak place here is afterwords process - list del levels most users not understand it. summing areas also (if we need total value area node not gives opportunity). also weakk place - dispatching after process instead vectorising pipeline.

Maybe two nodes -

1. simple for user to only areas calc, that utilize vertices also
2. list multimasking to nested list output.

[Durman]

[Durman]

I would not use monads so surely.

======================================================================
FAIL: test_monad_import (tree_import_tests.MonadImportTest)
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Traceback (most recent call last):
  File "/home/travis/build/nortikin/sverchok/installation/blender/2.82/scripts/addons/sverchok/tests/tree_import_tests.py", line 52, in test_monad_import
    JSONImporter.init_from_path(self.get_reference_file_path("monad_1.json")).import_into_tree(new_tree)
  File "/home/travis/build/nortikin/sverchok/installation/blender/2.82/python/lib/python3.7/contextlib.py", line 119, in __exit__
    next(self.gen)
  File "/home/travis/build/nortikin/sverchok/installation/blender/2.82/scripts/addons/sverchok/utils/testing.py", line 549, in assert_logs_no_errors
    self.assertFalse(has_errors, "There were some errors logged")
AssertionError: True is not false : There were some errors logged
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[nortikin]

ok