Modified MQTTComponent and MongoDB classes to be more robust.

MQTTComponent::publishMessage

• Ensures topic and message pointers are not null
• Ensures topic and message have not exceeded the max lengths

MongoDB::publish(batch)

MongoDB::publish(batch)::publishCurrentLine

• Added reconnection in the loop incase connection gets lost
• Prevents overflows by dropping oversized data
• Flags would-be overflows
• Logs packet size before publishing
• Treats CR/LF as EOL terminators when reconstructing batches
• Null-terminates each line