Add timezone support to ics-collector/lib for issue #19

[DeshDeepakKant]

Problem
Issue #19 - Calendar events not show correct timezone, so times look wrong in many calendar apps. Very confusing for users!

What I fix

• Add timezone info to events start time and end time
• Make sure Berlin timezone (Europe/Berlin) used when no timezone given
• Add special VTIMEZONE block that tell calendar apps about timezone rules
• Fix problem with summer time and winter time change
• Keep all-day events working good without timezone problems

How I do it

• Change ics-merger.php to make timezone block with summer/winter time info
• Update EventObject.php for handle timezone better
• Use Europe/Berlin as default when no timezone
• Keep original timezone when already there
• Make sure it work good with all-day events

Now events show correct time for everyone, no matter where they are! Calendar now have timezone info and work good in all apps.

[DeshDeepakKant]

@andibraeu please review it