refactored broad range of the application, split files, modularized calendar and file views, centralized bottom sheets and clipboard handling, and implemented unit test coverage

pubspec.yaml

@@ -71,6 +71,10 @@ dependencies:
   enough_icalendar: ^0.17.0
 
 dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  fake_async: ^1.3.1
+
   flutter_launcher_icons: ^0.14.3
   flutter_native_splash: ^2.4.4