libjpeg: import from oldpackages, add myself as maintainer, add fix for CVE-2013-6629, change PKG_LICENSE to SPDX identifier

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
libpng: import from oldpackages, add myself as maintainer, change PKG_LICENSE to SPDX identifiers, update to v1.2.51

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
libgd: import from oldpackages, add myself as maintainer, add license information, update to v2.1.0

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>