Make recurring period a database model

- For easier handling (foreignkeys, many2many)
- For higher flexibility (users can define their own periods)

uncloud_vm/models.py

@@ -71,12 +71,12 @@ class VMProduct(models.Model):
         return "Virtual machine '{}': {} core(s), {}GB memory".format(
                 self.name, self.cores, self.ram_in_gb)
 
-    @staticmethod
-    def allowed_recurring_periods():
-        return list(filter(
-            lambda pair: pair[0] in [RecurringPeriod.PER_365D,
-                RecurringPeriod.PER_30D, RecurringPeriod.PER_HOUR],
-            RecurringPeriod.choices))
+    # @staticmethod
+    # def allowed_recurring_periods():
+    #     return list(filter(
+    #         lambda pair: pair[0] in [RecurringPeriod.PER_365D,
+    #             RecurringPeriod.PER_30D, RecurringPeriod.PER_HOUR],
+    #         RecurringPeriod.choices))
 
 
     def __str__(self):