Make Facebook scheduler configurable

[ghostwriternr]

Right now, once started, the scheduler goes through every post in eternity and adds them to DB. On the next run, it does this all over again, which is unnecessary. This has 2 problems:

1. We only want the scheduler to fetch the latest 250 posts, say, after the DB is seeded the first time
2. In the current mode, new posts won't be fetched until the scheduler goes through every post. Until this is fixed, our feed will always be stale by around 5 days.