add hets dependencies formula

since we wouldn't want to install all these
haskell dependencies on every hets update, i've
added them as their own stand-alone formula.
correct the hets-dependencies formula.
add formula for pellet hets dependency.
add formula for the uDrawGraph hets dependency.
copy hets formula to hets_binary.
convert hets formula to a custom build formula.
add hets-lib formula.
fix hets-lib environment variable in hets.