[Android] Add LeakCanary

LeakCanary is a memory leak detection library which will run only in Debug mode.

android/app/build.gradle

     compile fileTree(dir: 'libs', include: ['*.jar'])
 
     implementation project(':sdk')
+
+    debugImplementation 'com.squareup.leakcanary:leakcanary-android:1.6.1'
+    releaseImplementation 'com.squareup.leakcanary:leakcanary-android-no-op:1.6.1'
 }

android/app/src/main/AndroidManifest.xml

       android:allowBackup="true"
       android:icon="@mipmap/ic_launcher"
       android:label="@string/app_name"
+      android:name=".MainApplication"
       android:theme="@style/AppTheme">
     <activity
         android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|screenSize|smallestScreenSize"

android/app/src/main/java/org/jitsi/meet/MainApplication.java

+/*
+ * Copyright @ 2018-present Atlassian Pty 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 org.jitsi.meet;
+
+import android.app.Application;
+
+import com.squareup.leakcanary.LeakCanary;
+
+/**
+ * Simple {@link Application} for hooking up LeakCanary:
+ * https://github.com/square/leakcanary
+ */
+public class MainApplication extends Application {
+    @Override
+    public void onCreate() {
+        super.onCreate();
+
+        if (!LeakCanary.isInAnalyzerProcess(this)) {
+            LeakCanary.install(this);
+        }
+    }
+}