Add class level (and filter on it)

stages/fixtures/test_fixture.json

@@ -20,12 +20,36 @@
       "name": "EDE"
     }
   }, 
+  {
+    "pk": 1, 
+    "model": "stages.level", 
+    "fields": {
+      "name": "1"
+    }
+  }, 
+  {
+    "pk": 2, 
+    "model": "stages.level", 
+    "fields": {
+      "name": "2"
+    }
+  }, 
   {
     "pk": 1, 
     "model": "stages.klass", 
     "fields": {
       "name": "1ASE3",
-      "section": 1
+      "section": 1,
+      "level": 1
+    }
+  }, 
+  {
+    "pk": 2, 
+    "model": "stages.klass", 
+    "fields": {
+      "name": "2ASE3",
+      "section": 1,
+      "level": 2
     }
   }, 
   {
@@ -138,6 +162,7 @@
     "fields": {
       "title": "Stage de pré-sensibilisation",
       "section": 1, 
+      "level": 1,
       "start_date": "2012-11-26", 
       "end_date": "2012-12-07"
     }