Add user-defined titles to subscriptions.
Implement editSubscription in GoogleReaderApi.
Use Set for user subscriptions.
Implement quickAdd URL.
Add default values for some DAO object fields.
Service and HTTP API refactoring.

- Discard AggregatorApi, not needed.
- Merge GoogleReaderApi into HttpApiActor.
- Move user-related operations out of HttpApiActor into UserService actor.