Ability to set timezone

[DavisNT]

Purpose

This is required by Mopidy-AlarmClock integration (https://github.com/woutervanwijk/Pi-MusicBox/issues/270).

Proposed solution

In web interface

• Take list of timezones from folder /usr/share/zoneinfo/ (may be there is better way to get list of timezones from OS)
• Store selected timezone in .ini file

In /opt/musicbox/startup.sh

• Read selected timezone from .ini file
• Ensure that /usr/share/zoneinfo/$TIMEZONE is a file
• echo $TIMEZONE > /etc/timezone
• rm -f /etc/localtime
• cp /usr/share/zoneinfo/$TIMEZONE /etc/localtime

The code snippet is untested.