Add script to kick sync for list of profiles

The infile should contain a JSON array of pids, eg:

    [
      "123@facebook",
      "456@twitter"
    ]

Right now it assumes pod 1, but we should have it load the profile row and get
the real one.
Make Dropbox page better

The files synclet was calling itself recursively and blocking up the whole
worker. Now it uses `nextRun` to page like everything else.