Rename FeedStrategy and its subclasses

[martindsq]

We have a FeedStrategy protocol that define functions and implement a collection of classes named Algorithms. Having two names is confusing, so lets stick with one of them. The pattern is named Strategy so we can use that, however @rabble mentioned that Algorithm feels more natural to him.

Also, this would be a nice time to check the functions defined as we have evolved to use swiftui and don't need some of them, counting the total number of items comes to my mind. Also, using the user id instead of user identity (like NoHopAlgorithm does) can be faster but seems less intuitive to use and not all algorithms use it, so we can get rid of that at the protocol level.