Email invitations

[mikedao]

Background: We want to be able to enter a user's Github handle and send them an email invite to our app. You'll use the Github API to retrieve the email address of the invitee.

As a registered user
When I visit /dashboard
And I click "Send an Invite"
Then I should be on /invite

And when I fill in "Github Handle" with <A VALID GITHUB HANDLE>
And I click on "Send Invite"
Then I should be on /dashboard
And I should see a message that says "Successfully sent invite!" (if the user has an email address associated with their github account)
Or I should see a message that says "The Github user you selected doesn't have an email address associated with their account."

The email should read as follows

Hello <INVITEE_NAME_AS_IT_APPEARS_ON_GITHUB>,

<INVITER_NAME_AS_IT_APPEARS_ON_GITHUB> has invited you to join <YOUR_APP_NAME>. You can create an account <here (should be a link to /signup)>.