Federated db column

As you may know the java server shares the database schema with the node.js server and I'd like to keep these in sync as much as possible to allow users to switch between implementation as they wish.

At present we don't support server sync in the java server. What this column would allow us to do is to clear out any data from external servers on start up.  The next time data is requested from an external server it is then pulled and stored locally.

This has a few advantages:

1) The java server can be more useful more quickly (no need to implement sync)
2) Data from channels no longer followed by anyone on the server are cleaned out
3) Potentially incorrect data (affiliations/subscriptions/items/etc) is completely fresh