datepicker should be easier to be aligned to the right

[jrencz]

now it calculates left and sets it as inline property so I have to use left: auto !important; right: 0 to make right border of the input and datepicker aligned. And as everyone should I'm trying to avoid !important as much as possible.
left: 0 may be set on class so it's easier to override it.
What's more: simple classes to stick the picker to the left or to the right may be provided.

[dvislov]

[lloiser]

[chrisirhc]

Duplicate of #1012