Start adding javadoc on public api of the SDK and move some files.

matrix-sdk-android/src/androidTest/java/im/vector/matrix/android/MainThreadExecutor.java

@@ -0,0 +1,34 @@
+/*
+ *
+ *  * Copyright 2019 New Vector Ltd
+ *  *
+ *  * Licensed under the Apache License, Version 2.0 (the "License");
+ *  * you may not use this file except in compliance with the License.
+ *  * You may obtain a copy of the License at
+ *  *
+ *  *     http://www.apache.org/licenses/LICENSE-2.0
+ *  *
+ *  * Unless required by applicable law or agreed to in writing, software
+ *  * distributed under the License is distributed on an "AS IS" BASIS,
+ *  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  * See the License for the specific language governing permissions and
+ *  * limitations under the License.
+ *
+ */
+
+package im.vector.matrix.android;
+
+import android.os.Handler;
+import android.os.Looper;
+
+import java.util.concurrent.Executor;
+
+public class MainThreadExecutor implements Executor {
+
+    private final Handler handler = new Handler(Looper.getMainLooper());
+
+    @Override
+    public void execute(Runnable runnable) {
+        handler.post(runnable);
+    }
+} 

matrix-sdk-android/src/androidTest/java/im/vector/matrix/android/session/room/timeline/TimelineHolderTest.kt

@@ -23,7 +23,7 @@ import androidx.test.annotation.UiThreadTest
 import com.zhuinden.monarchy.Monarchy
 import im.vector.matrix.android.InstrumentedTest
 import im.vector.matrix.android.LiveDataTestObserver
-import im.vector.matrix.android.api.thread.MainThreadExecutor
+import im.vector.matrix.android.MainThreadExecutor
 import im.vector.matrix.android.internal.session.room.members.RoomMemberExtractor
 import im.vector.matrix.android.internal.session.room.timeline.DefaultTimelineService
 import im.vector.matrix.android.internal.session.room.timeline.TimelineBoundaryCallback