Give activities names and log when entering and exiting them (#92)

## Summary

* Give activities name and log when entering and exiting them
* Clearer logs when attempting to debug, knowing where users are coming
from/going to helps

src/activities/reader/ReaderActivity.cpp

@@ -50,6 +50,8 @@ void ReaderActivity::onGoToEpubReader(std::unique_ptr<Epub> epub) {
 }
 
 void ReaderActivity::onEnter() {
+  ActivityWithSubactivity::onEnter();
+
   if (initialEpubPath.empty()) {
     onGoToFileSelection();
     return;