Option to post to Twitter on completion

[ZevEisenberg]

I get all my best ideas from QuickRadar.

[keith]

I think a pre-req to this is figuring out an interface for easily switching on and off the services you want to post to. There's an example of one solution to this from #45

Another possible pre-req to this, depending on how we want to do this, is #49 because if we want to allow disabling of Apple Radar (say because you posted to Apple Radar and forgot to post to Open Radar, so now you need to backfill to only Open Radar), we would still need the Radar ID.