Date/time picker + localization

The old calender date picker (which relied on Prototype) has been replaced with a jQuery one. (A majority of the files changed are just the removal of the old library and the addition of the new one). Localization is also dealt with for https://github.com/MarkUsProject/Markus/issues/102.

Date/time pickers have also been replaced on the spreadsheets form and the repo browser pages.