Add Email Confirmation to user registration

[mbramson]

When a user registers, send a confirmation email to the user that contains a link to confirm their account.

This is to prevent users from registering with emails that they don't actually have control of.

[austenmadden]

@mbramson Was there thoughts about which email library to use for this? I was looking at bamboo since it "seems" to be the best practice but am new to trying to accomplish practical tasks in Elixir/Phoenix.

Though there are simpler libraries that might be easier. Setting up something to actually send the email might also be tricky. I know there are services on heroku you can get to emulate an smtp sever/service or we could use a cloud email service.

[mbramson]

@austenmadden Pairmotron actually already uses Bamboo! Bamboo has been great. Very straightforward API. Pairmotron itself is already wired up to Mailgun for password reset emails.

See https://github.com/ElixirCLE/pairmotron/blob/master/lib/mailer/email.ex

[austenmadden]

Serves me right for not actually looking what was already in place. Thanks!