Closes #37

NOTE: this pull request is about log, so it spreads over most of the python files, I am not able to test everything (e.g. openhub driver, HPSUD mode) so more peer inspection or peer test is needed

This pull request removes the printd() method

    def printd(self, level, msg):        
        if self.logger:
            if level == 'warning':
                self.logger.warning(msg)
            elif level == 'error':
                self.logger.error(msg)
            elif level == 'info':
                self.logger.info(msg)
            elif level == 'exception':
                self.logger.exception(msg)
        else:
            if self.driver != "HPSUD":
                print("%s - %s" % (level, msg))

as it can be seen it has different problems:

• level is passed as string
• stardard logging levels, e.g. DEBUG, are missing
• if using a logger the logging level is respected, if not everything is printed to stdout discouraging developers to use debug, info and warning ...moreover in this only case the format is different
• "HPSUD mode" is without log and this is obtained accessing an "external object"

To obtain printd() flexibility, a single logger is instructed to use:

• FileHandler when -g option requires to save log to file
• StreamHandler for default behavious when log is written to stdout
• NullHandler when no log has to be written due to "HPSUD mode"

This "one-only-logger" approach enable all the log to use the same global settings for LOG LEVEL.

Having an effetive LOG LEVEL enables to change it via cli option, the --log_level has been introduced for this.

A single unique formatter is defined in advance.

Two info log line were added as proof of concept, they are one for loading of command definitions JSON file and the other for loading of command trasnlations CSV file.

Default level has been left as-is: ERROR.

In addition to log revision this pull request includes:

• little cosmetic fix, like typos
• a "help" improvement, now along each "non-writable" command description a " (readonly)" suffix is attached ...and this is because there are long more writable command than there are readonly command

Many things can be further improved, for instance:

• starting to log before and during options parsing
• introducing a method to write a message to stdout and log at the same time
• enabling logformatter to be read from conf file of cli option
• wrapping all the residual print("some message") to allow more control and avoid to mix them with real output (e.g. JSON)