[Feature Request] Rename Recorder and LogReward

Motivation

1. When dealing with logging, I found it hard to grasp how to use different loggers and classes. Especially, the Recorder makes it difficult to grasp the idea behind it.

2. For the LogReward class, I would love to make it more universal since it is actually just a class to log numeric values isn't it?

Solution

1. rename the Recorder to LogValidationReward since it basically does just that.
2. rename LogReward to LogScalar and give examples in the docs how to log the reward.

Alternatives

1. Include a validation step in the trainer with additional hooks that allow for validation based actions (just log validation metrics).
2. Add a LogScalar class from which LogReward inherits

Checklist

• I have checked that there is no similar issue in the repo (required)