"Source images" not sources of the images.

client: experimental is persistent in one session

Closes #2500

See merge request !1775

We need to keep an instance variable to the checkbox so we can uncheck
it again if they say "no".  Boo, instance variables are bad, but at
least its an underscore one...

Also, bring back "view cat" behind that toggle.  Fixes #2500.

Fix crash when updating rubrics

Closes #2508

See merge request !1782

Fixes #2508.

Some small fixes to WebPlom annotations

See merge request !1781

demo: GLOBIGNORE wasn't working

See merge request !1780

WebPlom annotations

See merge request !1756

Capture the list of files and filter out with grep.

django: Implement marking progress API

See merge request !1769

Calculate certainties for LAP predictions

Closes #2440

See merge request !1776

Test was failing because the cost_matrix -> probabilities argument
change was not reflected in test_IDreader.py

Fixes #2440

Certainty is calculated as the average of the digit probabilities of the
student ID number selected by the LAP solver. Thus, when LAP matches
Greedy, the certainties are the same, otherwise they differ.

The assemble_cost_matrix() is a helper function, so its invocation was
moved inside of lap_solver() in assign_prob.py, since lap_solver() needs
the heatmap probabilities as an argument for the certainty calculations.