Fix some issues reported by lintian

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

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/33/a6925f6fde45ded39c7f8527c93e8737007a8c.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/2a/d1c8a03a1e9f8a7dae8099b400fd38466006d0.debug

No differences were encountered between the control files of package **marsshooter**

No differences were encountered between the control files of package **marsshooter-data**

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

• Build-Ids: 2ad1c8a03a1e9f8a7dae8099b400fd38466006d0 33a6925f6fde45ded39c7f8527c93e8737007a8c

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Build and test logs for this branch can be found at https://janitor.debian.net/run/07ffd327-5116-44a0-b5c6-fef6ca757f24.