Various minor widgets updates

[kernc]

See commit log.

[ajdapretnar]

Seems relatively ok. Sometimes I have a hard time moving the centroid. The 'grab' icon is displayed (four directions) upon hover, but the centroid doesn't move. Only works after a couple of clicks. It also sometimes shows as if I'm about to hold the centroid, but when it fails to do so it adds a new centroid, which is annoying. But I suppose this is outside of this PR.

Can I merge even with the tests failing?

[codecov-io]

Codecov Report

Merging #30 into master will decrease coverage by <.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #30      +/-   ##
==========================================
- Coverage   98.29%   98.28%   -0.01%     
==========================================
  Files          13       13              
  Lines        1641     1637       -4     
  Branches      190      190              
==========================================
- Hits         1613     1609       -4     
  Misses         17       17              
  Partials       11       11

Impacted Files	Coverage Δ
orangecontrib/educational/widgets/owkmeans.py	97.08% <ø> (-0.03%)	:x:
.../educational/widgets/owpolynomialclassification.py	98.21% <ø> (-0.01%)	:x:
...gecontrib/educational/widgets/owgradientdescent.py	98.72% <100%> (-0.01%)	:x:

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[kernc]

The 'grab' icon is displayed (four directions) upon hover, but the centroid doesn't move.

Still a problem? Can't confirm, though, I changed much in that regard.

Please rename the PR (K-means updates is uninformative), and move unrelated commits into separate PRs.

Thanks, I was just testing stuff out in order to try to make the CI pass at least mostsome of the time. Wouldn't want to make early conclusions, but at the moment, shit is greeeeen!!! :green_salad:

[ajdapretnar]

The 'grab' icon is displayed (four directions) upon hover, but the centroid doesn't move.

Still a problem? Can't confirm, though, I changed much in that regard.

Not in a sense that I can replicate it. There's another issue with centroids, where I click in the neigbourhood of the centroid (no four directions icon) and when I start dragging, the centroid moves and upon release, a new centroid is created. Totally confusing.... I'm not sure what to do about this, but perhaps we can disallow creating new centroid with a click and allow simply setting the number of centroids and moving them around. However, this might impede teaching k-Means, so @BlazZupan needs to have an input as well. If he's fine with the current state, I'm fine too.

[BlazZupan]

I agree with Ajda: let's disallow the creation of new centroids by clicking on the pane.

[kernc]

Aware of this issue, I was sadly unable to figure it out in the short while. Opted for the proposed accepted solution instead. Thanks.