Bug 11598: Add --text option to overdue_notices similar to --html option

Bug 11598: Add --text option to overdue_notices similar to --html option

We have a number of reports of libraries that were upset by Bug 10720
being fixed! These libraries preferred this single file output, but as
text only. We should bring back this behavior, but as a feature, not a
bug.

Test Plan:
1) Apply this patch
2) Run overdue_notices.pl --html
3) Note the output is wrapped in html tags
4) Run overdue_notices.pl --text
5) Note the same output, but not wrapped in html tags

Signed-off-by: wajasu <matted-34813@mypacks.net>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
To test, add the -n parameter.
The filename generation could be refactored but not blocker.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>