[FIX] Annotator: Invalidate clusters on setting change

[VesnaT]

Issue

The widget crashes with

Traceback (most recent call last):
  File "/Users/vesna/orange-widget-base/orangewidget/gui.py", line 2258, in __call__
    self.func(**kwds)
  File "/Users/vesna/orange3-text/orangecontrib/text/widgets/owannotator.py", line 327, in __on_clustering_type_changed
    self._run()
  File "/Users/vesna/orange3-text/orangecontrib/text/widgets/owannotator.py", line 379, in _run
    self.graph.update_clusters()  # Remove cluster hulls and labels
  File "/Users/vesna/orange3-text/orangecontrib/text/widgets/owannotator.py", line 154, in update_clusters
    self._update_cluster_hull()
  File "/Users/vesna/orange3-text/orangecontrib/text/widgets/owannotator.py", line 162, in _update_cluster_hull
    hulls = self.master.get_cluster_hulls()
  File "/Users/vesna/orange3-text/orangecontrib/text/widgets/owannotator.py", line 525, in get_cluster_hulls
    return [(hull, colors[key])
  File "/Users/vesna/orange3-text/orangecontrib/text/widgets/owannotator.py", line 525, in <listcomp>
    return [(hull, colors[key])
IndexError: index 3 is out of bounds for axis 0 with size 3

To reproduce:
Corpus (book-excerpts) -> tSNE -> Annotated Corpus Maps (1. select Gaussian mixture models with 4 clusters, 2. select From variable)

Description of changes

• invalidate clusters if settings change

Includes

• Code changes
• Tests
• Documentation

[PrimozGodec]

/rebase

[codecov-commenter]

Codecov Report

Merging #910 (068315b) into master (1a384dc) will increase coverage by 0.08%.
The diff coverage is 50.00%.

❗ Current head 068315b differs from pull request most recent head 9522847. Consider uploading reports for the commit 9522847 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #910      +/-   ##
==========================================
+ Coverage   77.07%   77.15%   +0.08%     
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  Files          86       86              
  Lines       12037    12039       +2     
  Branches     1578     1578              
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+ Hits         9277     9289      +12     
+ Misses       2453     2448       -5     
+ Partials      307      302       -5