Add support for setting the TimeZone of the WeekView

[jwiese]

In my use case, I'm showing a calendar for events that happen in a particular timezone, which might not be the same as the user's current timezone, so I added the ability to set the timezone on the WeekView object.

[alamkanak]

Calendar objects (of the WeekViewEvent class) are more than capable of handling the timezones. You can manipulate the timezone of events to make them appear in week view in whatever timezone you want. Why should the timezone be an attribute of the view itself?

[jwiese]

Well, at least one reason is because the setShowNowLine is then going to show the wrong place on the timeline. Another reason is that goToToday won't work properly across days (e.g. it's already tomorrow in Korea, so if the event is in Korea and the user is in San Francisco, then goToToday should really go to my home timezone's "tomorrow".

It's OK with me if you don't want to accept the pull request, since I was able to make the changes and they work well for my own app. I just thought it might be useful to others. Great work, btw, this is a very helpful library.