MAJOR: General improvements

Description

New backend methods and frontend components to allow folders to be renamed and deleted
Added new 404 error page
Added new ErrorBoundary component to show when there is a Frontend React error
Added checking to see if the user is signed in for all pages
Added ability to sign out
Added ability to delete flashcards
BREAKING: Changed get-flashcards so it reads flashcard data from your own flashcard data list. It now needs the user ID in the API request
Made disabled buttons unclickable
A valid access link is required to sign in to the frontend

Issue where the XP, streak and heatmap were not updated when a user revised cards

BREAKING: jwtToken (the json web token provided by create-account) is now passed instead of userID to all functions, allowing for greater security

[ ] Does backend/database/database_config.py have the type of production?
[ ] Does frontend/src/api/config.js have the correct server url, reading from the deployed instance at http://dolphinflashcards.com/api/?
[ ] If not merging development to main, is the MR title prefixed with MAJOR, MINOR or PATCH?
[ ] Has backend/__init__.py been updated with the relevant version, following the semantic versioning standard
[ ] Has CHANGELOG.md been updated to explain the new version?