MKCalendarView's first day based on user's locale + minor bugfix.

Hello,

If you think it would be helpful, this pull request changes the behaviour of `MKCalendarView` so that if a left-most day isn't specified in the initializer the current locale's calendar is queried for the correct value, rather than assuming Sunday. If a day that isn't Sunday or Monday is returned, it assumes Monday.

0c87ada also fixes a minor bug where if a `TKCalendarMonthViewController` is initialized using `initWithTimeZone:`, the timezone argument is ignored.

If you decide you want the bugfix without the default behaviour changed, I'd be happy to refactor that into its own request.

Cheers