Implemented support for date+time in TimeSlider

fixes #211 

Rendering date+time if the range is less than a day but still spanning over two dates. Add tests for the previous cases and clarified code to make it easier to read.

I changed the CSS for the slider to fit the date+time, by taking some space from the slider-part, to make sure the view component maintains the same size overall.

Example screenshot of how it renders (it switches to the 15th at the end of the animation, be patient ;)).
![timeslider-date-and-time](https://cloud.githubusercontent.com/assets/978461/5110276/a412d06a-7017-11e4-80c2-025761dd2aea.gif)