Slight Refactoring, Documentation Improvements, and Minor Bugfixes

Default/Example Configuration

• Switch Chrome/Chromium Thumbnails type from file to directory.
• Don't merge Chromium Thumbnails into Chrome Thumbnails.

Documentation

• Fulfils some more Core Infrastructure Documentation Best Practices.
  • Document how to report security bugs by (PGP-encrypted) e-mail.
  • Document PGP key(s) used in the project and how to retrieve it.
• Add repology package list badges to README.md + docs/installation.md.

Test Suite Changes

Adds new test/build dependency Perl::Critic.

• Test suite: Run checkbashism also on share/common.sh and Xsession.d/25unburden-home-dir-xdg.
• Test suite: Provide checkbashism as its own Make target.
• Use Perl::Critic as part of the test suite.
  • Add libtest-perl-critic-perl as build-dependency.
  • Add .perlcriticrc* files to configure Perl::Critic.

Code Refactoring

Adds new dependencies IPC::Run and Try::Tiny.

• Make Test::UBH perlcritic-severity-4-clean.
• Make unburden-home-dir perlcritic-severity-4-clean.
  • Solved by minor refactorings.
• Make unburden-home-dir perlcritic-severity-3-clean.
  • Use IPC::Run's run() instead of backticks for calling lsof.
    • Add according dependencies on libipc-run-perl.
  • Use /x flag on all regular expressions and sprinkle blanks over them.
  • Use HEREDOC instead of multiline quoted strings.
  • Don't use capture variables outside a regexp without a test.
  • Use Try::Tiny instead of eval { ...; }; if ($@) { ...; }.
    • Add according dependencies on libtry-tiny-perl.
  • Raise Perl::Critic's max_mccabe values slightly by 5.
  • Ignore ErrorHandling::RequireCarping (no module) and
    ControlStructures::ProhibitCascadingIfElse (compact enough).

Debian Packaging

• Set Rules-Requires-Root: no.
• Set Multi-Arch: foreign for unburden-home-dir-doc as suggested by the Multi-Arch hinter.