ca-certificates: new package

CA certificates used for SSL based applications.  The package installs CA
certificates to /usr/share/ca-certificates and creates symbolic links under
/etc/ssl/certs.  For example, the existing libcurl package will use these
certificates for https urls.  Based on the debian ca-certifcates package.

[Peter: fixup comments as pointed out by Yann]
Signed-off-by: Martin Bark <martin@barkynet.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>