[PierreRaybaut]

Closes #455.

Depends on DataLab-Platform/SigimaX#31 (downsampling threshold), which closes DataLab-Platform/SigimaX#30. The DataLab CI tests this PR against the SigimaX branch of the same name.

Problems

• Auto downsampling only started above 5 times the configured maximum number of points (fixed in SigimaX). With the default value of 100,000, signals of up to 500,000 points were drawn in full.
• Since v1.0.0 (a9b540f), changing the sig_autodownsampling* or sig_linewidth* settings called manual_refresh(), which only refreshes the selected signals:
  • the other curves kept the former settings, even once selected again (a selection change does not update the plot items);
  • plot items made from them for dialogs (make_item(update_from=...)) inherited the stale settings.
• The Settings dialog and the documentation gave 10,000 as the default maximum number of points, whereas the actual default value is 100,000.

Changes

Settings applied to all curves

• New BasePlotHandler.update_existing_items():
  • it updates all existing plot items from their objects and the current settings;
  • unlike refresh_plot("existing"), it neither changes the visibility of the items nor adds the shape items again.
• DLMainWindow.__edit_settings calls it when a sig_autodownsampling* or sig_linewidth* option changes, instead of manual_refresh().

Settings dialog

• Actual default value of Downsampling max points (100,000).
• Clearer help: maximum number of points displayed; data are not modified.

Documentation and translations

• Settings documentation: display only, actual default value.
• Release notes for 1.4.0 (Bug Fixes, Signal display).
• French translations (UI and documentation). Only the entries changed by this PR are updated: running the translation scan in a working copy containing build/lib/datalab adds unrelated stale strings.

Before / after

Number of points drawn, with only the 2M-point signal selected when the settings are changed:

Step	150k pts	300k pts	600k pts	2M pts
Before: creation (max 100,000)	150,000	300,000	100,000	100,000
Before: max set to 10,000	150,000	300,000	100,000	10,000
After: creation (max 100,000)	75,000	100,000	100,000	100,000
After: max set to 10,000	10,000	10,000	10,000	10,000

Tests

• New datalab/tests/features/signal/autodownsampling_unit_test.py, covering, through the Settings action:
  • the default value shown by the Settings dialog;
  • auto downsampling settings (maximum, disabling, enabling) applied to unselected curves;
  • line width applied to unselected curves;
  • visibility and number of plot items unchanged (no duplicated shape items);
  • plot items made for dialogs using the current settings.
• 4 of these 5 tests fail without the fix. The fifth one guards the new method against duplicated shapes.
• Local run of features/signal, features/common and backbone: 838 passed, 1 skipped.
• The new tests also pass with the min/max downsampling of Min/max curve downsampling preserving peaks PlotPyStack/PlotPy#85 (at most maxpoints + 2 points drawn).