Add model for period.

biscuit/apps/chronos/models.py

+from django.db import models
+from django.utils.translation import ugettext_lazy as _
+
+
+class TimePeriod(models.Model):
+    WEEKDAY_CHOICES = [
+        (0, _('Sunday')),
+        (1, _('Monday')),
+        (2, _('Tuesday')),
+        (3, _('Wednesday')),
+        (4, _('Thursday')),
+        (5, _('Friday')),
+        (6, _('Saturday'))
+    ]
+
+    weekday = models.PositiveSmallIntegerField(verbose_name=_(
+        'Week day'), choices=WEEKDAY_CHOICES)
+    period = models.PositiveSmallIntegerField(
+        verbose_name=_('Number of period'))
+    time_start = models.TimeField(verbose_name=_('Time the period starts'))
+    time_end = models.TimeField(verbose_name=_('Time the period ends'))
+
+    def __str__(self):
+        return '%s, %d. period (%s - %s)' % (self.weekday, self.period, self.time_start, self.time_end)