Replace date and time pickers with a bootstrap one

(This PR includes the changes in https://github.com/tangentlabs/django-oscar/pull/1455, also see there for the merge conflict.)

This replaces the date and time picker widgets. In usability tests our customers ignored or didn't understand the time sliders at all. Also the pickers were visually a bit different from the rest of the dashboard.

This PR replaces all three (date, time, datetime) pickers with http://www.malot.fr/bootstrap-datetimepicker/demo.php.

Initially I used http://jdewit.github.io/bootstrap-timepicker/ for the timepicker because I wasn't sure how much work it takes to make the malot datetime picker into a time picker. It turns out that one patch was needed for correct I18N.

This PR also adds localization for the month and day names in the calendar widget.

Then it changes all picker inputs to the component form. A `TimePickerInput` class was added for use with `TimeField`s in other oscar implementations (like ours^^) - oscar doesn't have a `TimeField` anywhere.