Remove `extern loglevel_e loglevel` from Logger

The log level is currently defined using a global variable in the Logger.h file using the extern keyboard. Since Logger.h is a library (libUtils), the declaration of the loglevel variable has to be done in each program depending labRemote. Even if the logger is not used explicitely.

The proposal is to change the loglevel variable from an external to a static object. That way it does not have to be declared in all programs.