libgd: moved to github

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

git-svn-id: svn://svn.openwrt.org/openwrt/packages@41468 3c298f89-4303-0410-b956-a3cf2f4a3e73
libpng: moved to github

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

git-svn-id: svn://svn.openwrt.org/openwrt/packages@41469 3c298f89-4303-0410-b956-a3cf2f4a3e73
libjpeg: moved to github

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

git-svn-id: svn://svn.openwrt.org/openwrt/packages@41470 3c298f89-4303-0410-b956-a3cf2f4a3e73