POPPY-0011: Document and refactor the logger

1. The logger is not documented. Thus, we should describe it more detailed.

2. Some parts of the logger (mainly syslog) is very hard to read due to the strange class names. Try to improve it.

Start by locating the logger implementation and its syslog-related classes, then review the existing documentation and the class names that are described as difficult to read. Done means the logger is documented in more detail and the unclear class names have been improved.

Written by the indexing model from the issue text.