Redesign home screen (#166)

## Summary

* Redesigned home screen with big option to continue reading and
slightly nicer options to navigate to core sections
* Attempt to use the cached EPUB details (title, author) if they exist,
otherwise fall back to file name
* Adjusted button hints on home screen, removed Back option and changed
left/right to up/down

## Additional Context

* Core of this work comes from @ChandhokTannay in
1d36a86ef1

src/activities/home/HomeActivity.h

@@ -13,6 +13,8 @@ class HomeActivity final : public Activity {
   int selectorIndex = 0;
   bool updateRequired = false;
   bool hasContinueReading = false;
+  std::string lastBookTitle;
+  std::string lastBookAuthor;
   const std::function<void()> onContinueReading;
   const std::function<void()> onReaderOpen;
   const std::function<void()> onSettingsOpen;