LibCrypto: Fix issues in the Crypto stack

This commit fixes up the following:
- HMAC should not reuse a single hasher when successively updating
- AES Key should not assume its user key is valid signed char*
- Mode should have a virtual destructor
And adds a RFC5246 padding mode, which is required for TLS

Libraries/LibCrypto/Cipher/Mode/CBC.h

@@ -36,6 +36,7 @@ namespace Cipher {
     template <typename T>
     class CBC : public Mode<T> {
     public:
+        virtual ~CBC() {}
         template <typename... Args>
         explicit constexpr CBC<T>(Args... args)
             : Mode<T>(args...)