Jupyter: ERP5 kernel sends code using POST

Query strings used on GET requests have size limitations
on servers and this causes big code cells to not be executed
at all, returning only an Internal Server Error with no
further explanation.

/reviewed-by @kirr, @Tyagov (on nexedi/slapos!43)

software/ipython_notebook/software.cfg

@@ -43,7 +43,7 @@ md5sum = d7d4a7e19d55bf14007819258bf42100
 [erp5-kernel]
 <= download-file-base
 filename = ERP5kernel.py.jinja
-md5sum = e6d7d9cee8095fb8788af3c6d82b9b6f
+md5sum = 3dfc6a7c16828bff55dec4cf96b730d3
 
 [kernel-json]
 <= download-file-base

software/ipython_notebook/template/ERP5kernel.py.jinja

@@ -172,11 +172,11 @@ class ERP5Kernel(Kernel):
     """
 
     try:
-      erp5_request = requests.get(
+      erp5_request = requests.post(
         self.url,
         verify=False,
         auth=(self.user, self.password),
-        params={
+        data={
           'python_expression': code,
           'reference': self.reference,
           'title': self.title,