Modernize sample keys and sample configs

I kept most of the certificate properties equal to the old
certs, since some people's test scripts might rely on them (and
it does not require any creativity from my part).

Changes:
 * Add script to generate fresh test/sample keys
   (but keep sample keys in git for simple testing)
 * Switch from 1024 to 4096 bits RSA CA
 * Switch from 1024 to 2048 bits client/server RSA keys
 * Switch from 1024 to 2048 bits Diffie-Hellman parameters
 * Generate EC client and server cert, but sign with RSA CA
   (lets us test EC <-> RSA interoperability)
 * Remove 3DES cipher from 'sample' config
 * Add 'remote-cert-tls server' to client config
 * Update config files to deprecate nsCertType in favour of the
   keyUsage and extendedKeyUsage extensions.
 * Make naming more consistent

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <54721611.4020103@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9271
Signed-off-by: Gert Doering <gert@greenie.muc.de>