Rework PG error/warning/debug message handling.

[drgrice1]

The PG messages are now dealt with completely separately from the webwork2 general warning handling. Furthermore PG warnings and debug messages are separately dealt with.

The PG internal_debug_messages are no longer dealt with at all. They are unnecessary and inappropriately named, and will be removed from PG.

Also, handling of the warnings is now much more consistent in all of the different places that problems are rendered. In fact, they all use the new templates/ContentGenerator/Base/problem_warning_and_debug_output.html.ep template for this.

All of this output is no longer wrapped in a code tag. That is the wrong thing for this. None of it is code. It also causes problems with openwebwork/pg#1384.

[drgrice1]

Note that this pull request is necessary to test openwebwork/pg#1386. However, this pull request does not require that one. So this pull request can be tested with @somiaj's pull request referenced above.

[drgrice1]

Here is a problem you can use to test the various warnings:

DOCUMENT();
loadMacros('PGstandard.pl', 'PGML.pl', 'PGcourse.pl');

# This is a general Perl warning obviously.
warn 'warning issued from problem';

$a    = Compute(3);
$aCmp = $a->cmp;

BEGIN_PGML
[% This issues a PGalias.pm file not found warning. %]
[!image not found!]{'invalid-image.png'}{300}

[_]{ name => 'badAnswerName' }
END_PGML

NAMED_ANS('badAnswerName', $aCmp);

# This issues a PGresponsegroup::insert_response undefined or empty response
# label warning.
INSERT_RESPONSE('badAnswerName');

# This issues a PGresponsegroup::insert_response existing answer label warning.
INSERT_RESPONSE('badAnswerName', 'badAnswerName', 6);

# This issues a PGresponsegroup::extend_response response label not provided
# warning.
EXTEND_RESPONSE('badAnswerName');

# This issues a PGresponsegroup::extend_response invalid value type warning.
EXTEND_RESPONSE('badAnswerName', 'badAnswerName', 6);

ENDDOCUMENT();

[drgrice1]

Also, you can test debugging messages with the check boxes that appear when viewing a problem in a set as an admin user. You can also test debugging messages with @somiaj's pull request and a problem that has formula diagnostics enabled.

[somiaj]

Looks good.