Fix -Werror failures and release 0.2019pre.0/0.2019pre.0-0co1

Make GCC 8 happy.

• Package release 0.2019pre.0-0co1
  • TODO: run gbp buildpackage --git-tag --git-tag-only --git-ignore-branch when landing this commit
• Release Traprain 0.2019pre.0
  • TODO: run git tag v0.2019pre.0 when landing this commit
• client/navigation: Actually unref items when freeing routes
• test-routing-request: Use the right unref function
• debian/rules: Make compiler warnings non-fatal

Apply the tags and build with ~/apertis-customizations/development/build-snapshot localhost -d ../deb from the SDK.