Fix some issues reported by lintian

Fix some issues reported by lintian

• Bump debhelper from old 11 to 13. (package-uses-old-debhelper-compat-version)
• Set debhelper-compat version in Build-Depends. (uses-debhelper-compat-file)
• Set upstream metadata fields: Bug-Database, Bug-Submit, Repository-Browse. (upstream-metadata-file-is-missing, upstream-metadata-missing-bug-tracking)
• Update standards version to 4.4.1, no changes needed. (out-of-date-standards-version)
• Trim trailing whitespace. (trailing-whitespace)
• Set upstream metadata fields: Repository. (upstream-metadata-missing-repository)

Debdiff

These changes affect the binary packages:

[The following lists of changes regard files as different if they have different names, permissions or owners.]

Files in second set of .debs but not in first

-rw-r--r--  root/root   /usr/lib/debug/.build-id/3b/7f380bf50ec8e469460b254961830d244e8cf2.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/9b/ceb2f5fd3f21d4f6d038659eabef7c73f9514f.debug

No differences were encountered between the control files of package **ptunnel-ng**

Control files of package ptunnel-ng-dbgsym: lines which differ (wdiff format)

• Build-Ids: 9bceb2f5fd3f21d4f6d038659eabef7c73f9514f 3b7f380bf50ec8e469460b254961830d244e8cf2

You can also view the diffoscope diff (unfiltered).

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Build and test logs for this branch can be found at https://janitor.debian.net/run/4c73e536-55be-4fc3-8d04-46ad932ec0e1.