LaTeX packages for tables in PG

This pull request needs to be approved at the same time as two related pull requests in pg and libraries. The three pull requests do as follows:

In webwork2, certain latex packages are added to hardcopyPreamble.tex
In pg, pccTables.pl is replaced with niceTables.pl, with significant enhancements.
In libraries, several PCC macro files are added, and pccTables.pl redirects to niceTables.pl