refactor error handling: get validation error information from a form attribute instead of req.data to avoid pb when multiple forms are displayed

use yams.schema method for initial value

merge

Use of datetime instead of mx.datetime and use of new date_range.

Use widget TextInput instead of DateTimePicker.

Fix date_range increments argument.

ensure format is not an unicode string

should prefill cached values for relation in the primary or secondary category

cleanup

use values cached on the entity if any

update old_calendar, more needed

import cleanup