Storing sensor data locally

[KyleBenson]

The event reporter should store data locally (SD card?) in addition to reporting it via the Internet. This should essentially be a queue, where old data is archived and then eventually removed to make room when a certain database size is reached (configurable parameter). This should especially work when in an offline mode, and so should keep track of whether data has been reported or not for when regaining network connectivity.

[KyleBenson]

Andy and I were just talking and think we should also do this for the local neighbors in the mesh network in some way. Maybe only one hop away?

[bfrggit]

Now I have a local MySQL based version in my cycle fork. We can try to merge these changes back to our repo later. Maybe some time after the June demo?

This is briefly how it works:
Event reporter only send a event to the MySQL event sink when the event is not published to any "normal" event sink (send method returns False).
There's another MySQL database maintainer class in my fork that periodically read from database for unpublished events, and publish them. If an event is from database, it will have a database tag as an attribute, which contains its table id. That table id will be used later to update the database to mark this event as published.