User email-requests

* Users can invite others to join their team with email
* Users can sign up for site by entering token through email
I would have written this class like so:

```ruby
class PlayerEmailCollection
  include Enumerable

  def initialize(email_addresses)
    @email_addresses = email_addresses.spli
  end

  def each(&block)
    email_addresses.each(&block)
  end

  private

  attr_reader :email_addresses
end
```