Email once account is approved

[lyannne]

ℹ️ Issue

Closes #227

📝 Description

1. Added method to send email to user if their account is approved, basically used the same method in notifications
2. Moved addUserToGroup methods to user folder
3. Implemented removing user from group before adding them to a new one
4. Checked that user is moving from Inactive to Employee before sending email, since that is the only case a user should receive a verification email.
5. Added onClick to both buttons in frontend, so the backend should be called when an admin clicks the buttons to approve/reject a user (assuming that the name field is the username that will be used when calling the addUserToGroup and delete backend route).

✔️ Verification

N/A

Test Changes

Changed a few tests to pass checks for the PR.

🏕️ (Optional) Future Work / Notes

Abstracting the backend functions, double checking that this actually works