Some changes to allow more customization

Hello Dmitry, Hello Ronny,

As you probably are already aware, I dabbled a little bit with your project. I don't know, if you're agreeable with the changes I made, but have a look yourself. Most important points:

* I decoupled the date picker from the date view, so users can subclass/replace the built-in DIDatePickerDateView
* The date view is now configurable via a dictionary exposed via the date picker, allowing for configuration of fonts and colors
* the size of the date view is now declared by the view class
* the space between the views is now configurable at runtime via a property
* I left the current APIs implementing a subset of this intact, so there hopefully won't be no impact to existing users. But as the version number is quite low, we could also discuss just to leave them out.

What do you think?

Best Regards,
Martin