Add tests

[aeatencio]

We should add some regression tests for:

• src/models/ao_message.cr
• src/models/call.cr
• src/models/reply_command.cr
• src/models/simulator_command.cr
• src/models/simulator.cr
• src/models/verboice.cr
• src/controllers/call_controller.cr
• src/controllers/incoming_phone_numbers_controller.cr
• src/config.cr
• src/db.cr