Fix some issues reported by lintian

Fix some issues reported by lintian

• Use secure copyright file specification URI. (insecure-copyright-format-uri)

• Use secure URI in Homepage field. (homepage-field-uses-insecure-uri)

• Bump debhelper from old 12 to 13. (package-uses-old-debhelper-compat-version)

• Set upstream metadata fields: Bug-Database, Bug-Submit, Repository, Repository-Browse. (upstream-metadata-file-is-missing, upstream-metadata-missing-bug-tracking, upstream-metadata-missing-repository)

• Fix field name case in debian/copyright (files => Files).

• Use canonical URL in Vcs-Browser, Vcs-Git. (vcs-field-not-canonical)

This merge proposal was created automatically by the Janitor bot. For more information, including instructions on how to disable these merge proposals, see https://janitor.debian.net/lintian-fixes.

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The bot will automatically update the merge proposal to resolve merge conflicts or close the merge proposal when all changes are applied through other means (e.g. cherry-picks). Updates may take several hours to propagate.

Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/slic3r-prusa/062bf19d-c4ac-43b3-82d3-c0de9e782bfd.

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/11/62c1b7ea5c236b6d54d0e4fe9436b455a2c504.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/0c/e840a1f422195aa35c97b7174927d56ae82f8b.debug

Control files of package prusa-slicer: lines which differ (wdiff format)

• Homepage: http​://github.com/prusa3d/slic3r https​://github.com/prusa3d/slic3r

Control files of package prusa-slicer-dbgsym: lines which differ (wdiff format)

• Build-Ids: 0ce840a1f422195aa35c97b7174927d56ae82f8b 1162c1b7ea5c236b6d54d0e4fe9436b455a2c504

Control files of package slic3r-prusa: lines which differ (wdiff format)

• Homepage: http​://github.com/prusa3d/slic3r https​://github.com/prusa3d/slic3r

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