Initial stab at linking up email.
Adds basic email functionality: a traveler receives an email confirmation that their booking has been submitted.
Merge branch 'master' of https://github.com/MarcGarreau/the_pivot into link-up-email
Sends order notification to user.
Creates a REQUESTED state, and moves email notifications to that state.
Sends each host an email notifying them of a booking request.
Merge pull request #104 from MarcGarreau/link-up-email

Link up email

Tests passing for me.