-Added debug preference settings for debug and beta builds.

-Removed leak canary toggle on app menu.
-Added leak canary settings to debug preference.
-Removed/renamed leak canary related strings.

app/src/main/res/menu/debug_menu.xml

@@ -1,12 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<menu xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:app="http://schemas.android.com/apk/res-auto">
-
-    <item android:id="@+id/action_toggle_heap_dump"
-        android:orderInCategory="9999"
-        android:checkable="true"
-        android:title="@string/toggle_leak_canary"
-        android:visible="true"
-        app:showAsAction="never"/>
-
-</menu>