Remove hardcoded strings

## Overview

Certain files to do with the UI include hard-coded strings, which do not take internationalisation into account.

For example, the following code snippet will always show the same text "An error occurred while attempting to retrieve the task item's details. Please try again later." regardless of device language:

https://github.com/EdricChan03/StudyBuddy-android/blob/b530689bbfe59a1e80f77c15a86251076e852f29/app/src/main/java/com/edricchan/studybuddy/ui/modules/task/EditTaskActivity.kt#L61-L65