lib.log: introduce a new rotating filehandler

[onkelandy]

considering current date and time as filenames. IMPORTANT: docu needs to be updated for the operationlog and datalog plugin

Ways to test:

handlers:
    datetime_file1:
        (): lib.log.DateTimeRotatingFileHandler
        formatter: shng_detail
        when: 'M'
        interval: 1
        backupCount: 2
        filename: ./var/log/testlog.log
        encoding: utf8
    datetime_file2:
        (): lib.log.DateTimeRotatingFileHandler
        formatter: shng_detail
        when: 'M'
        interval: 1
        backupCount: 5
        filename: /{year}/test-{year:02}-{month}-{day}-{hour:02}.{minute:02}
        encoding: utf8