add leak canary for detecting memory leaks at debug builds

app/build.gradle

@@ -40,6 +40,10 @@ dependencies {
     compile 'com.github.chrisbanes:PhotoView:1.3.1'
     compile 'it.sephiroth.android.exif:library:1.0.1'
     compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+
+    debugCompile 'com.squareup.leakcanary:leakcanary-android:1.5'
+    releaseCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.5'
+    testCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.5'
 }
 
 buildscript {

app/src/main/AndroidManifest.xml

@@ -7,6 +7,7 @@
     <uses-permission android:name="android.permission.SET_WALLPAPER"/>
 
     <application
+        android:name=".App"
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_launcher_name"

app/src/main/kotlin/com/simplemobiletools/gallery/App.kt

@@ -0,0 +1,14 @@
+package com.simplemobiletools.gallery
+
+import android.app.Application
+import com.squareup.leakcanary.LeakCanary
+
+class App : Application() {
+    override fun onCreate() {
+        super.onCreate()
+        if (LeakCanary.isInAnalyzerProcess(this)) {
+            return
+        }
+        LeakCanary.install(this)
+    }
+}