Squashed commit of the following:

commit ff25e2dc285c423f4c40a83deb89a56ee62b15a9
Author: Alban Gruin <alban dot gruin at gmail dot com>
Date:   Sat Feb 11 13:47:38 2017 +0100

    Nettoyage du code de CourseManager

commit 26a132d5d1fdb7fc9da827bbc9d5e409834fb954
Author: Alban Gruin <alban dot gruin at gmail dot com>
Date:   Sat Feb 11 13:45:14 2017 +0100

    Suppression du GroupedManager et de toutes ses sous-classes

1 files changed, 0 insertions, 80 deletions

diff --git a/db.py b/db.py
deleted file mode 100644
index 94df376..0000000
--- a/db.py
+++ /dev/null
@@ -1,80 +0,0 @@
-#    Copyright (C) 2017  Alban Gruin
-#
-#    celcatsanitizer is free software; you can redistribute it and/or modify
-#    it under the terms of the GNU General Public License as published by
-#    the Free Software Foundation; either version 2 of the License, or
-#    (at your option) any later version.
-#
-#    celcatsanitizer is distributed in the hope that it will be useful,
-#    but WITHOUT ANY WARRANTY; without even the implied warranty of
-#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-#    GNU General Public License for more details.
-#
-#    You should have received a copy of the GNU General Public License along
-#    with celcatsanitizer; if not, write to the Free Software Foundation, Inc.,
-#    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
-
-from django.db import connections
-from django.db.models import Manager
-from django.db.models.functions import Extract
-from django.db.models.sql.compiler import SQLCompiler
-from django.db.models.sql.query import Query
-from django.db.models.sql.where import WhereNode
-from django.db.models.query import QuerySet
-
-class ExtractWeek(Extract):
-    lookup_name = "week"
-
-
-class GroupedCompiler(SQLCompiler):
-    def get_group_by(self, select, order_by):
-        result = super(GroupedCompiler, self).get_group_by(select, order_by)
-        expressions = []
-        for expr in self.query.real_group_by:
-            ref = expr if hasattr(expr, "as_sql") else self.query.resolve_ref(expr)
-            sql, params = self.compile(ref)
-            result.append((sql, params))
-
-        return result
-
-
-class GroupedQuery(Query):
-    def __init__(self, model, where=WhereNode):
-        super(GroupedQuery, self).__init__(model, where)
-        self.real_group_by = []
-
-    def clone(self, klass=None, memo=None, **kwargs):
-        obj = super(GroupedQuery, self).clone(klass, memo, **kwargs)
-        obj.real_group_by = self.real_group_by[:]
-        return obj
-
-    def add_grouping(self, *grouping):
-        self.real_group_by.extend(grouping)
-
-    def clear_grouping(self):
-        self.real_group_by = []
-
-    def get_compiler(self, using=None, connection=None):
-        if using is None and connection is None:
-            raise ValueError("Need either using or connection")
-        if using:
-            connection = connections[using]
-        return GroupedCompiler(self, connection, using)
-
-
-class GroupedQuerySet(QuerySet):
-    def __init__(self, model=None, query=None, using=None, hints=None):
-        super(GroupedQuerySet, self).__init__(model, query, using, hints)
-        self.query = query or GroupedQuery(self.model)
-
-    def group_by(self, *field_names):
-        obj = self._clone()
-        obj.query.clear_grouping()
-        obj.query.add_grouping(*field_names)
-        return obj
-
-
-class GroupedManager(Manager):
-    def __init__(self):
-        super(GroupedManager, self).__init__()
-        self._queryset_class = GroupedQuerySet