[Security] Use a CSPRNG for salts, tokens, and RNG seeding

Password salts and activation tokens were generated with the global SFMT
RNG, which was seeded from a 32-bit timestamp, making registration
salts and activation tokens predictable. The game RNG used the same
timestamp seed across restarts.

Add CryptoUtil backed by OpenSSL RAND_bytes and use it for salt/token
generation and to seed RNG_SFMT with a 64-bit CSPRNG value in both the
client and server. Link libcockatrice_utility against OpenSSL::Crypto.

Took 30 seconds

Took 25 minutes

libcockatrice_utility/libcockatrice/utility/cryptoutil.cpp

@@ -0,0 +1,25 @@
+#include "cryptoutil.h"
+
+#include <openssl/rand.h>
+
+namespace CryptoUtil
+{
+QByteArray randomBytes(int count)
+{
+    QByteArray bytes(count, '\0');
+    if (RAND_bytes(reinterpret_cast<unsigned char *>(bytes.data()), count) != 1) {
+        // Randomness failure is fatal: never fall back to a predictable source.
+        qFatal("CryptoUtil::randomBytes: RAND_bytes failed");
+    }
+    return bytes;
+}
+
+quint64 randomUInt64()
+{
+    quint64 value;
+    if (RAND_bytes(reinterpret_cast<unsigned char *>(&value), sizeof(value)) != 1) {
+        qFatal("CryptoUtil::randomUInt64: RAND_bytes failed");
+    }
+    return value;
+}
+} // namespace CryptoUtil