Update plots to work with latest ggplot.

Also add scaffold for plotting CDFs. So far there exist only functions
for generating CDFs of discrete distributions. They still need some
tuning, e.g., the y-axis doesn't start at 0 yet, and adjusting the line
type doesn't work either.
Do not recompile figures if they exist.
Add missing qualifiers.
Add inverse transform sampling.

This needed some rearranging of other content, such as the conjugate
prior tables.