Added evaluation into Day 4

Table_of_Contents.ipynb

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@@ -100,7 +100,7 @@
      "level": 2,
      "metadata": {},
      "source": [
-      "Day 4: Matrix Factorization"
+      "Day 4: Matrix Factorization and Evaluation"
      ]
     },
     {
@@ -108,7 +108,10 @@
      "metadata": {},
      "source": [
       "1.  [Nonnegative Matrix Factorization](notebooks/nmf.ipynb)\n",
-      "1.  [Exercise: Source Separation using NMF](exercises/nmf_source_separation.ipynb)"
+      "1.  [Exercise: Source Separation using NMF](exercises/nmf_source_separation.ipynb)\n",
+      "1.  [Classification of Separated Signals](notebooks/classify_separated_signals.ipynb)\n",
+      "1.  [Cross Validation](notebooks/cross_validation.ipynb)\n",
+      "1.  [Evaluation](notebooks/evaluation.ipynb)"
      ]
     },
     {
@@ -123,8 +126,6 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "1.  [Cross Validation](notebooks/cross_validation.ipynb)\n",
-      "1.  [Evaluation](notebooks/evaluation.ipynb)\n",
       "1.  [Tonal Descriptors: Pitch and Chroma](notebooks/tonal.ipynb)\n",
       "1.  [Feature Extraction](notebooks/feature_extraction.ipynb)\n",
       "1.  [Beat Tracking](notebooks/beat_tracking.ipynb)\n",