Fix some issues reported by lintian

Fix some issues reported by lintian

• Trim trailing whitespace. (trailing-whitespace)
• Bump debhelper from old 11 to 13. (package-uses-old-debhelper-compat-version)
• Set upstream metadata fields: Bug-Database, Bug-Submit, Repository-Browse. (upstream-metadata-file-is-missing, upstream-metadata-missing-bug-tracking)
• Update standards version to 4.6.1, no changes needed. (out-of-date-standards-version)
• Remove field Section on binary package libgxr-0.15-0 that duplicates source. (installable-field-mirrors-source)

This merge proposal was created by the Janitor bot, and it will automatically rebase or close this proposal as appropriate when the target branch changes. Any comments you leave here will be read by the Janitor's maintainers.

Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/gxr-openvr/3ac71db7-497c-431c-9edd-d5d2ef8625fe.

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/7e/256afd9ad3e632addb14d2a91990292c2d3ac0.debug
-rw-r--r--  root/root   /usr/lib/debug/.build-id/e2/ae6d9d2cbd7d1e3ab17acb5d9e2865fed5d777.debug
-rw-r--r--  root/root   /usr/lib/debug/.dwz/x86_64-linux-gnu/libgxr-0.15-0.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/69/89d422ada342bd9802b0144aeaf3d2cfd62705.debug
-rw-r--r--  root/root   /usr/lib/debug/.build-id/b7/1d04b5c710333fb40673e2e13e3ba5e44d1a58.debug

No differences were encountered between the control files of package **libgxr-0.15-0**

Control files of package libgxr-0.15-0-dbgsym: lines which differ (wdiff format)

• Build-Ids: 6989d422ada342bd9802b0144aeaf3d2cfd62705 b71d04b5c710333fb40673e2e13e3ba5e44d1a58 7e256afd9ad3e632addb14d2a91990292c2d3ac0 e2ae6d9d2cbd7d1e3ab17acb5d9e2865fed5d777

No differences were encountered between the control files of package **libgxr-dev**

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