support for unpacking megolm keys

This is incredibly hacky at the moment, pending the arrival of ephemeral
events, but it kinda works.

lib/crypto-algorithms/megolm.js

@@ -65,16 +65,6 @@ MegolmEncryption.prototype._ensureOutboundSession = function() {
 
     var key = this._olmDevice.getOutboundGroupSessionKey(session_id);
 
-    console.log(
-        'Created outbound session. Add with window.mxMatrixClientPeg.' +
-            'matrixClient._crypto._olmDevice.addInboundGroupSession("' +
-            [
-                this._roomId, this._olmDevice.deviceCurve25519Key, session_id,
-                key.key, key.chain_index
-            ].join('", "') +
-            '")'
-    );
-
     this._olmDevice.addInboundGroupSession(
         this._roomId, this._olmDevice.deviceCurve25519Key, session_id,
         key.key, key.chain_index
@@ -170,6 +160,30 @@ MegolmDecryption.prototype.decryptEvent = function(event) {
     }
 };
 
+/**
+ * @inheritdoc
+ *
+ * @param {module:modules/event~MatrixEvent} event key event
+ */
+MegolmDecryption.prototype.onRoomKeyEvent = function(event) {
+    console.log("Adding key from ", event);
+    var content = event.getContent();
+
+    if (!content.room_id ||
+        !content.session_id ||
+        !content.session_key ||
+        content.chain_index === undefined
+       ) {
+        console.error("key event is missing fields");
+        return;
+    }
+
+    this._olmDevice.addInboundGroupSession(
+        content.room_id, event.getSenderKey(), content.session_id,
+        content.session_key, content.chain_index
+    );
+};
+
 base.registerAlgorithm(
     olmlib.MEGOLM_ALGORITHM, MegolmEncryption, MegolmDecryption
 );