[FIX] SOM: Store selection Settings in list instead of np.ndarray

[PrimozGodec]

Issue

The orange widget base does not support settings with type np.ndarrray

Traceback (most recent call last):
  File "../orange-canvas-core/orangecanvas/application/canvasmain.py", line 1612, in save_swp
    if not document.isModifiedStrict() and undoStack.isClean():
  File "../orange-canvas-core/orangecanvas/document/schemeedit.py", line 664, in isModifiedStrict
    node_properties(self.__scheme)
  File "../orange-canvas-core/orangecanvas/document/schemeedit.py", line 2538, in node_properties
    scheme.sync_node_properties()
  File "../orange-widget-base/orangewidget/workflow/widgetsscheme.py", line 99, in sync_node_properties
    if settings != node.properties:
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Description of changes

Store SOM's settings in a list instead.

Includes

• Code changes
• Tests
• Documentation