Incorporate local timezone in jam recorder folder

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In an effort to have Jamulus log entries match up with associated jam recorder folder names (without having to manually calculate UTC offsets), it is proposed that the jam recorder folder names incorporate local timezone rather than UTC timezone. The current recording functionality uses UTC date/time only - currentDateTimeUtc(). This would involve revising jamrecorder.cpp to use local timezone date/time - currentDateTime().

To illustrate the problem, current jam recorder folder names are based on UTC time, whereas the associated log entry that initiates the recording is logged using local time. For example:

"Folder Jam-20200423-185758274" - corresponds to log entry - "23.4.2020, 11:57:58, 70.67.70.31, connected"

An alternative solution, as proposed by corrados, is to give users the choice of using either local or UTC timezone in the recorder folder name by using server command-line parameters as per the following comments:

https://github.com/jamulussoftware/jamulus/issues/497#issuecomment-670702534
> "Could we somehow encode that information in the given string? E.g.
> ./Jamulus -s -R [ltz]/home/test/jamulusrecordings
> So that we parse the directory name for a given "[ltz]" at the beginning. Not the nicest solution but would work.

https://github.com/jamulussoftware/jamulus/issues/497#issuecomment-670841260
> We already have command line arguments with combined informations. For consistency to these, we should use this format instead:
> ./Jamulus -s -R "localtimezone;/home/test/jamulusrecordings"
> I.e. we use a ";" as a separator."

Also, having both the jam recorder folder and corresponding log file entry presented in standard ISO format (yyyy-MM-dd HH:mm:ss) would also be helpful to match the two up.

Original post and discussion with detailed example - [sourceforge post](https://sourceforge.net/p/llcon/discussion/server/thread/bdc3c34844/?limit=25#e0c9), have the recorder folder name reflect the current date/time of the local timezone.

Inizia da jamrecorder.cpp e confronta i percorsi currentDateTimeUtc() e currentDateTime(). Esamina quindi il parsing della riga di comando server -R e la discussione correlata per determinare se è prevista l’ora locale, UTC o una modalità selezionabile. Il lavoro è completo quando i nomi delle cartelle del recorder e i timestamp dei log possono essere messi in corrispondenza senza calcolare manualmente l’offset, usando un formato concordato.

Scritto dal modello di indicizzazione a partire dal testo della issue.