Invitations don't check to see if the user has already been invited, if you're provided a CSV to send to mass invite a bunch of users, the API doesn't check to see if those users with specified emails already exist in the org.
Acceptance criteria:
[ ] back end changes to locate duplicate email addresses and fail if one is located
[ ] front-end modal to inform if duplicate is found.
Invitations don't check to see if the user has already been invited, if you're provided a CSV to send to mass invite a bunch of users, the API doesn't check to see if those users with specified emails already exist in the org.
Acceptance criteria: