[FIX] Hierarchical clustering: Make annotation a context setting

[janezd]

Alternative to #1739.

Issue

OWHierarchialClustering: Annotation drop down does not keep context settings.

Description of changes

Annotation index is replaced with a context setting that contains an attribute or a string. Context are used only if the data are distances between rows. Otherwise, separate settings for axis=0 and axis=1 are used.

Settings are not migrated: the previous settings didn't work anyway.

Includes

• Code changes
• Tests
  - [ ] Documentation

[codecov-io]

Current coverage is 88.86% (diff: 100%)

Merging #1748 into master will not change coverage

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[VesnaT]

Values in the combo should be the same when placing a widget on canvas (disconected) and after disconnecting data from it.

[VesnaT]

I think selection in the combo, when data are distances between columns, should be somehow saved as well.

[janezd]

• Empty widget should have Enumeration as default.
• If domain has a class, use it as default, otherwise Names, otherwise Evaluation.

[astaric]

Would it be possible to add a tests that checks that the settings are stored and retrieved? Both, for row an attribute distances?

[janezd]

The widget already implemented the above rules we discussed with @VesnaT: class was chosen if it existed, and Enumeration was preferred over None. The latter didn't work (and an empty widget had None instead of Enumeration) because of the bug in gui.comboBox, which is fixed in #1764. Fetch my repo and cherry pick bb88aad if you want to test.

Widget now behaves like in #1739: it has context settings for matrices with attached data, and separate settings for axis=0 and axis=1.

I added tests.

(Note to self: ea30352 is the commit with the previous version.)

[VesnaT]

Make a workflow: File (iris) -> Select columns -> Distances -> Hieararhical Clustering.
It works fine. Than use Select Columns to remove Target Variable from domain. After clicking "Send", Hieararhical Clustering crashes.

[janezd]

@VesnaT, thanks. Fixed (lines 997 and 998 in the revised commit) and tested (test_domain_loses_class).