Small adjustment to plots and ops

Small changes so too lazy to open two separate MRs, sorry:

• The title of a plot is never used (at least not in plotIt). For 1D plots, it makes sense to use the title by default as the x axis title.

• Add unary operators to number proxies. Notably, this allows to use treeoperations.Sort to sort in descending order: simply return -x in the sorting lambda instead of x.

• Add trigonometric function ops

• Division of float proxies did not work (?), fixed.

• Fix switch op