Alarm motion event database

[mxmaxime]

• closes Save motion even in database #40
• closes Add "device_id" to MQTT motion detect messages #21 we need it to link the motion detection even to the Device. Thanks to this, we know where we have motion, and we can tell it to the resident and so one.
• closes Assign a client_id for all MQTT program #20 now we have the device_id field (Add "device_id" to MQTT motion detect messages #21) we can use it for mqtt client id, because they have to be unique. In the future we could have multiple instance of these piece of software, so we use device_id in client_id to ensure it to be unique 👍
• closes Camera class is loosing mqtt connection and then publish is ignored #45 thanks to the commit c853fae Basically, we start a thread to handle mqtt network related stuffs thanks to the call of self.mqtt_client.loop_start() and we start/initialize mqtt client in start method and not in the class constructor, otherwise it's not working silently, no errors but doesn't work. This method is called in a Thread, because this class is executed by a Thread when the alarm is up.
• closes Motion detected message + picture in one mqtt publish #44

Remaining questions

What to save in database

Please see issue #70

[mxmaxime]

Good to go.