Jupyter: Use mime_type from content_result before displaying anything from frontend.

This fix is for bug https://nexedi.erp5.net/bug_module/20160212-76EAAC/view?ignore_layout:int=1
where the image base64 string was only shoeing. The error in this case was that the mime_type
of content code_result was not being updated by the kernel before display.

Reported by : @ivan

software/ipython_notebook/software.cfg

@@ -43,7 +43,7 @@ md5sum = d7d4a7e19d55bf14007819258bf42100
 [erp5-kernel]
 <= download-file-base
 filename = ERP5kernel.py.jinja
-md5sum = 3dfc6a7c16828bff55dec4cf96b730d3
+md5sum = eb07520fc189dcac2d3bd2db1368b1ba
 
 [kernel-json]
 <= download-file-base

software/ipython_notebook/template/ERP5kernel.py.jinja

@@ -265,7 +265,25 @@ class ERP5Kernel(Kernel):
             mime_type = 'text/plain'
             try:
               content = json.loads(self.response)
+
+              # Example format for the json result we are expecting is :
+              # content = {
+              #            "status": "ok",
+              #            "ename": null,
+              #            "evalue": null,
+              #            "traceback": null,
+              #            "code_result": "",
+              #            "mime_type": "text/plain"
+              #            }
+              # So, we can easily use any of the key to update values as such.
+
+              # Getting code_result for succesfull execution of code
               code_result = content['code_result']
+
+              # Update mime_type with the mime_type from the http response result
+              # Required in case the mime_type is anything other than 'text/plain'
+              mime_type = content['mime_type']
+
             # Display to frontend the error message for content status as 'error'
               if content['status']=='error':
                 reply_content = {