[TESTS] Adding delete test

test_parser_ngramextractor.ipynb

 {
  "metadata": {
   "name": "",
-  "signature": "sha256:cd05544202c3cb00384c1d21f5f7383ee29eccb208aa49467e726fc15c331ee8"
+  "signature": "sha256:df3d60ee3db86cfa96ad9f0cfbd6b55c075a84ca08e52b566913b10ba2bcf0b3"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -19,7 +19,7 @@
      "language": "python",
      "metadata": {},
      "outputs": [],
-     "prompt_number": 10
+     "prompt_number": 1
     },
     {
      "cell_type": "code",
@@ -41,9 +41,7 @@
     {
      "cell_type": "code",
      "collapsed": false,
-     "input": [
-      "project_type = NodeType.objects.get(name=\"Project\")"
-     ],
+     "input": [],
      "language": "python",
      "metadata": {},
      "outputs": [],
@@ -56,12 +54,13 @@
       "from node.models import Project\n",
       "from django.contrib.auth.models import User\n",
       "user = User.objects.get(username=\"alexandre\")\n",
+      "project_type = NodeType.objects.get(name=\"Project\")\n",
       "Project(user=user, type=project_type, name=\"Abeilles\").save()"
      ],
      "language": "python",
      "metadata": {},
      "outputs": [],
-     "prompt_number": 46
+     "prompt_number": 3
     },
     {
      "cell_type": "code",
@@ -473,12 +472,23 @@
      "cell_type": "code",
      "collapsed": false,
      "input": [
-      "Corpus.objects.all().delete()"
+      "from node.models import Corpus, Project\n",
+      "Project.objects.all()\n",
+      "Corpus.objects.all()"
      ],
      "language": "python",
      "metadata": {},
-     "outputs": [],
-     "prompt_number": 45
+     "outputs": [
+      {
+       "metadata": {},
+       "output_type": "pyout",
+       "prompt_number": 7,
+       "text": [
+        "[<Corpus: Abeilles>]"
+       ]
+      }
+     ],
+     "prompt_number": 7
     },
     {
      "cell_type": "code",
@@ -492,13 +502,13 @@
       {
        "metadata": {},
        "output_type": "pyout",
-       "prompt_number": 48,
+       "prompt_number": 5,
        "text": [
         "[<Node: Abeilles>]"
        ]
       }
      ],
-     "prompt_number": 48
+     "prompt_number": 5
     },
     {
      "cell_type": "code",