Merge the matrix-java-sdk due to it no longer maintained. Remove thirdparty repositories.

src/main/java/io/kamax/matrix/_MatrixContent.java

@@ -0,0 +1,41 @@
+/*
+ * matrix-java-sdk - Matrix Client SDK for Java
+ * Copyright (C) 2017 Kamax Sarl
+ *
+ * https://www.kamax.io/
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package io.kamax.matrix;
+
+import java.net.URI;
+import java.net.URL;
+import java.util.Optional;
+
+public interface _MatrixContent {
+
+    URI getAddress();
+
+    URL getPermaLink();
+
+    boolean isValid();
+
+    Optional<String> getType();
+
+    byte[] getData();
+
+    Optional<String> getFilename();
+
+}