Strip whitespace from start and end of each field when importing classlist files

Replace line 48 of /opt/webwork/webwork2/lib/WeBWorK/File/Classlist.pm

        my $csv = Text::CSV->new({ binary => 1 }); # binary for utf8 compat

by the two lines

        my $csv = Text::CSV->new({ binary => 1, allow_whitespace => 1 });
	   # binary for utf8 compat, allow_whitespace to strip all whitespace from start and end of each field

This fixes the bug in reading classlist files when e.g. someone has a space before or after a status (e.g. ,C  ,)
and later gets an error when e.g. assigning sets to the new student becasue of an unknows status