Refactors keystore.h type aliases.

This squashed commit either encapsulates type alias declarations at the appropriate scope; or removes type aliases that are not used.

The encapsulated type aliases are declared using C++11's `using` notation in favor of the `typedef` notation.

src/wallet/crypter.h

@@ -126,6 +126,8 @@ private:
     bool fDecryptionThoroughlyChecked;
 
 protected:
+    using CryptedKeyMap = std::map<CKeyID, std::pair<CPubKey, std::vector<unsigned char>>>;
+
     bool SetCrypted();
 
     //! will encrypt previously unencrypted keys