Datepicker update

- Updated Datepicker to v1.3.0
- Updated CSS (Added compiled file, the source is in LESS format)
- Updated HTML where the datepicker is used
- Fixed JS function in scripts.js which was interfering with the new datepicker
- Removed readonly markings (hope it's ok, I think it also looks cleaner now)
- Fixes #54: Calendar overlap issue
Could you please integrate the datepicker.css directly into the styles.css file?