Implement megolm encryption/decryption

Very early attempt at encryption/decryption implementation via megolm. You have
to c&p the keys manually.

lib/crypto-algorithms/index.js

@@ -22,6 +22,7 @@ limitations under the License.
 var base = require("./base");
 
 require("./olm");
+require("./megolm");
 
 /**
  * @see module:crypto-algorithms/base.ENCRYPTION_CLASSES