* Create Redisable

* Use #redis instead of Redis.current

- Rename Mastodon::TimestampIds into Mastodon::Snowflake for clarity
- Skip for statuses coming from inbox, aka delivered in real-time
- Skip for statuses that claim to be from the future

* Wrap methods of ProcessFeedService::ProcessEntry in classes

This is a change same with 425acecfdb15093a265b191120fb2d4e4c4135c4, except
that it has the following changes:

* Revert irrelevant change in find_or_create_conversation
* Fix error handling for RemoteActivity

* Introduce Ostatus name space