UTF-8 hardcopy support using xelatex, polyglossia, fontspec, xunicode (replaces part of PR#972)

[taniwallach]

This replaces the hardcopy part of #972 without the Docker config modifications.

Summary of changes:

• Includes xelatex hardcopy themes for English and English+Hebrew as samples (28 new files)
• 3 modified files:
  • conf/localOverrides.conf.dist contains sample code to use the new themes.
  • conf/site.conf.dist reinserts the $externalPrograms{pdflatex} setting as it was removed in commit bea85e1 apparently by accident.
  • lib/WeBWorK/ContentGenerator/Hardcopy.pm - the code which displays the available hardcopyThemes options was changed to avoid the use of maketext.
    • Local installations may have local hardcopyThemes and they will not have entries in the PO translations files, and the prior code would trigger errors as a result.

Discussion of testing can be found in #972 .

@nmoller reviewed at #972 (review)

Testing with Hebrew requires using xelatex instead of pdflatex and having all of the following installed:

• the culmus Hebrew fonts,
• LaTeX pakages: polyglossia, fontspec, xunicode

Note: The version of xelatex and various latex packages in Ubuntu 16.04 did not manage to compile the Hebrew+English latex files I tested, but they compiled under Ubuntu 18.04 with the same packages.

As noted at #972 (comment) the change to use xelatex and to add the extra hardcopy themes can be done (by hand) in course.conf for a specific course.

[taniwallach]

@nmoller @heiderich - This is the hardcopy part of the old PR. Please check so we can merge it.

[taniwallach]

I'm merging this in based on the prior testing in the previous multi-topic PR, as I am about to post a call for testing in the forums.

• There is exactly one line of production code changed:
  • dropping a maketext call in lib/WeBWorK/ContentGenerator/Hardcopy.pm
  • which is required to allow local additions of new hard-copy themes not to break things.
• There are 28 new files (4 new hard-copy themes, each a set of 7 files in a new directory under conf/snippets/hardcopyThemes/) which cannot cause trouble unless someone decides to try them out.
• There are 2 changes to conf.dist files:
  • In conf/site.conf.dist to put back a critical line someone accidentally deleted.
  • In conf/localOverrides.conf.dist to enable the use of the new hard-copy themes, which can be added to an operational conf/localOverrides.conf or left out.