Twilio setup with test credentials.
Merge branch 'ggp-sprint2-endtoend' of github.com:guidance-guarantee-programme/prototypes into ggp-sprint2-endtoend
Enable sessions.
Store contact details in the session.
Store booked slots in the session.
Preview contact details and booked slots.
Confirm booking and send SMS.

_Note_: Using Twilio test number.
Display booked slots in confirmation view.