Highlight terms during Leibniz selection

[ghost]

At the moment, Leibniz propagation informs the user of what terms it's going to use during propagation in a clumsy side-panel. The side-panel should maybe stay (?), but this is different from how the user receive selection information everywhere else in the program: it's typically displayed on the grid by highlight draws.

We should also perform highlight draws during Leibniz selection.