Initial Implementation of Subscriber and Scheduler

[JoashCWK]

Structured as follows:

Event Handler: main class called from main.cpp

• Contains MqttClient and MsgProcessor

MqttClient: mqtt client interface

MsgProcessor

• Contains DbAccessor
• processes MqttMessage to check for the topic, then take action accordingly (host server to get new device MAC address, call DbAccessor, save schedule in crontab, etc.).
• Any computation needed (e.g., getting DateTime, TaskSchedule, DeviceInfo) should be done here.

DbAccessor: read from/write to DB

• should interface with objects from util directly rather than the low level strings/ints

[JoashCWK]

Still some pending work to be done, but separate tickets have been created for them. From an end-to-end basis, this PR seems complete so will merge and close now.