Improve and extend log_text / log_rules for item logging

[onkelandy]

• added some more options such as time, date, now
• added possibility to implement the value of an item in the log text (e.g. for updating the message)
• added possibility to define all log_rules by an item instead of a distinct value
• some minor improvements These updates should make (together with logging.yaml) datalog, memlog and operationlog obsolete.