set cell_type properly first-class in the Cell object

- in toJSON
- don't clobber existing value in Cell constructor

IPython/html/static/notebook/js/cell.js

@@ -52,7 +52,7 b' var IPython = (function (IPython) {'
         // same order. Easiest is to create and set to null in parent class.
 
         this.element = null;
-        this.cell_type = null;
+        this.cell_type = this.cell_type || null;
         this.code_mirror = null;
 
 
@@ -201,6 +201,7 b' var IPython = (function (IPython) {'
     Cell.prototype.toJSON = function () {
         var data = {};
         data.metadata = this.metadata;
+        data.cell_type = this.cell_type;
         return data;
     };
 

IPython/html/static/notebook/js/codecell.js

@@ -444,7 +444,6 b' var IPython = (function (IPython) {'
     CodeCell.prototype.toJSON = function () {
         var data = IPython.Cell.prototype.toJSON.apply(this);
         data.input = this.get_text();
-        data.cell_type = 'code';
         // is finite protect against undefined and '*' value
         if (isFinite(this.input_prompt_number)) {
             data.prompt_number = this.input_prompt_number;

IPython/html/static/notebook/js/textcell.js

@@ -276,7 +276,6 b' var IPython = (function (IPython) {'
      */
     TextCell.prototype.toJSON = function () {
         var data = IPython.Cell.prototype.toJSON.apply(this);
-        data.cell_type = this.cell_type;
         data.source = this.get_text();
         if (data.source == this.placeholder) {
             data.source = "";
@@ -357,7 +356,7 b' var IPython = (function (IPython) {'
         var that = this;
         this.element.focusout(
                 function() { that.auto_highlight(); }
-            );
+        );
     };
 
     RawCell.options_default = {