Add extra placeholders for Matrix ID room invites notifications

- Sender display name, if available
- Room name, if available

src/main/java/io/kamax/mxisd/backend/memory/MemoryIdentityStore.java

@@ -1,6 +1,6 @@
 /*
  * mxisd - Matrix Identity Server Daemon
- * Copyright (C) 2018 Maxime Dor
+ * Copyright (C) 2018 Kamax Sarl
  *
  * https://www.kamax.io/
  *
@@ -76,6 +76,11 @@ public class MemoryIdentityStore implements AuthenticatorProvider, IDirectoryPro
         return cfg.isEnabled();
     }
 
+    @Override
+    public Optional<String> getDisplayName(_MatrixID mxid) {
+        return findByUsername(mxid.getLocalPart()).map(MemoryIdentityConfig::getDisplayName);
+    }
+
     private UserDirectorySearchResult search(
             Predicate<MemoryIdentityConfig> predicate,
             Function<MemoryIdentityConfig, UserDirectorySearchResult.Result> mapper