Bug 16357: Use separate Log4Perl logger for each Plack app

Bug 16357: Use separate Log4Perl logger for each Plack app

This patch creates separate timestamped Log4Perl loggers
for each Plack app, so that the Intranet, OPAC, and API are logged
to separate files.

To Test:
0) apt-get install libplack-middleware-logwarn-perl
1) Apply "Alternative" patches
2) Copy PLACK block from etc/log4perl.conf to
/etc/koha/sites/kohadev/log4perl.conf and replace __LOG_DIR__ appropriately
3) Copy debian/templates/plack.psgi to /etc/koha/sites/kohadev/plack.psgi
4) Temporarily add 'warn "TEST"' to opac-main.pl and mainpage.pl
5) koha-plack --restart kohadev
6) Go to /cgi-bin/koha/mainpage.pl and /cgi-bin/koha/opac-main.pl
7) Open /var/log/koha/kohadev/plack-opac-error.log and
/var/log/koha/kohadev/plack-intranet-error.log
7) Observe a log line like the following:
[2020/06/22 03:51:23] [WARN] TEST at <SCRIPT and line #>.

Signed-off-by: Arthur Suzuki <arthur.suzuki@biblibre.com>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>