[DaysOfWeek] Improved Detection of best Date Style

Another Pull Request. I need the automatic sizing since the calendar is not always fullscreen in my application. Figured it might be a good addition. Tell me if there is something to be improved and or needs to be changed.
Anyways hope you like it.

 Malte

Detailed List of Changes:
- Added Enum to differentiate the DaysOfWeekStyles
- Added displayStyle Function, which return the DisplayStyle to use. Can
be overridden in subclasses.
- Added Algorithm to automatically choose the right DisplayStyle based
on frame size instead of orientation.
- Moved the Label (Re-)Generation to the updateWeekdayLabels function.
- Edited the dayOfWeekLabelFont method so it always return the same font
Size regardless of the device orientation
- removed (now unnecessary) methods to detect the Device Type and
Orientation.