Improved: working with variable calendar padding

I tried to customize datepicker layout but found one vexatious limitation: `.datepicker_calendar` padding is hardcoded in the `jquery.simple-dtpicker.js` and it is difficult to make smooth layout with another padding (see attached image) without script hacking.
I fixed it using px-trimming solution from [here](http://stackoverflow.com/a/1100653/1051870).