Allow to pass level argument to logs sub-command

Created by: M5oul

Like:

duniter logs --loglevel trace

This supposes to have a different logging implementation, because the logs command plugs to the duniter.log file, which have its own log level which might be different than the level asked.

For example the file logs can be defined with duniter config --loglevel info, which is not compliant with duniter logs --loglevel trace. The traces won't be displayed, because they do not exist in the file.