Resolve "sysadmin can retrieve phone number list from cli" (#38)

Closes #38 (closed)

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Overview:

• provide a GET /phoneNumbers endpoint:
  • returns phone number count and list of phone numbers (including twilio sid)
  • allows caller to filter by active/inactive phone numbers
• hit this endpoint from boost list_numbers, adding new --active / --inactive flags

Implementation details:

• add twilioSid to phoneNumber model, persist it upon phone number creation