Kalium micro-optimizations

[DavidMS73]

• Remove unused resources. For example, in accounts_sheet.dart, avatar.dart, send_complete_sheet.dart, appstate_container.dart, settings_drawer.dart and nanoutil.dart, there are imports that are not being used.
• Use indexed loops instead of iterator and for-each loops: by creating unnecessary objects, you are taking up more memory space and this can make the application run slower, so it is recommended to change the "for in of the objects" to a "for of index".