Fix some issues reported by lintian

Fix some issues reported by lintian

• debian/copyright: use spaces rather than tabs to start continuation lines. (tab-in-license-text)
• Refer to common license file for Apache-2.0. (copyright-does-not-refer-to-common-license-file, copyright-not-using-common-license-for-apache2)
• 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, Repository, Repository-Browse. (upstream-metadata-file-is-missing, upstream-metadata-missing-repository)

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/libswingx-java/0278779c-387f-4cbb-b7ec-b1b6ddb9c955.

These changes have no impact on the binary debdiff.

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