[ENH] canvas/add-ons: Add extra packages via a name input dialog

[FIX] Add-ons working again (PyPI JSON interface + local official index)

Move report to widget namespace

[FIX] Fix variable type guessing

* Preserve `original_values` to pass to `guess_data_type`.
* Add a namask argument to it.

settings: include SettingProvider in __all__

[ENH] Variable lists (with QListView) optimizations

[FIX] Addon dialog crashes when site-packages directory does not exist

i.e. when used to display dynamic content

... when the displayed model is empty.

The default implementations in QAbstractListItemModel is sufficient
and faster ('index' in particular is on a hot path in the Qt
model/view framework so it needs to be fast)

... where used to select variable length (large) models.

[FIX] Fix reading double quoted text fields

PermissionError is just one of possible errors that can be raised from
failed open attempt. When one of the other erorrs occurs, an error was
shown (as can be seen on sentry)

module members not included in __all__ are considered private.
SettingProvider is used in widgets to declare subcomponents and should
therefore be included in __all__.

[FIX] Sieve Diagram: Fix spacing of axis labels

[FIX] Fix data reading speed

Kmeans test timeout

[FIX] KMeans clear results on k change, do not recluster