fix #302, add a toggle for disabling leak canary

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

@@ -4,11 +4,14 @@ import android.app.Application
 import com.squareup.leakcanary.LeakCanary
 
 class App : Application() {
+    val USE_LEAK_CANARY = false
     override fun onCreate() {
         super.onCreate()
+        if (USE_LEAK_CANARY) {
             if (LeakCanary.isInAnalyzerProcess(this)) {
                 return
             }
             LeakCanary.install(this)
         }
     }
+}