feat: wakeup target detection (#731)

## Summary

* If going to sleep was from the Reader view, wake up to the same book.
Otherwise, wakeup to the Home view

src/activities/Activity.h

@@ -23,4 +23,5 @@ class Activity {
   virtual void loop() {}
   virtual bool skipLoopDelay() { return false; }
   virtual bool preventAutoSleep() { return false; }
+  virtual bool isReaderActivity() const { return false; }
 };