Add SMS reminders

[swoloszynski]

Integrate SMS API with custom auto-reminder command from https://github.com/swoloszynski/kitcat/issues/7

• [x] Receive SMS message on personal (test) phone number
• [x] Run custom command to receive SMS reminders only for due or overdue connections
• [x] Filter due and overdue to only incomplete

[swoloszynski]

Useful for testing: https://mock.readthedocs.org/en/latest/ https://www.toptal.com/python/an-introduction-to-mocking-in-python