Fix some issues reported by lintian

Changes-By: lintian-brush
Fixes: lintian: out-of-date-standards-version
See-also: https://lintian.debian.org/tags/out-of-date-standards-version.html

Changes-By: lintian-brush
Fixes: lintian: renamed-tag
See-also: https://lintian.debian.org/tags/renamed-tag.html

Changes-By: lintian-brush
Fixes: lintian: package-uses-old-debhelper-compat-version
See-also: https://lintian.debian.org/tags/package-uses-old-debhelper-compat-version.html

enable cross building of packages with build-deps on this one

by loosening some of its dependencies

as per the Multiarch hinter

Fixes lintian: field-name-typo-dep5-copyright
See https://lintian.debian.org/tags/field-name-typo-dep5-copyright.html for more details.

Fixes lintian: homepage-field-uses-insecure-uri
See https://lintian.debian.org/tags/homepage-field-uses-insecure-uri.html for more details.

Fixes lintian: debian-watch-uses-insecure-uri
See https://lintian.debian.org/tags/debian-watch-uses-insecure-uri.html for more details.

cppreference-doc (20170409-1.1) unstable; urgency=medium

  * Build using Qt5 (Closes: #874862)

Upstream version 20170409

Add gbp config