[Printer] Fix major bug. See below for more explanations :

Before, I used request.session to store some information about the current jobs to be printed.
This was because in the very beginning, I had an issue with disappearing files in my model.

I was able to fix this issue in a previous commit, but I still needed the jids.
However, because of this storage system, if someone tried to print a file, then oppened a second tab,
and tried to print anoter file, he/she would pay twice for the second file ....

I decided to add a hidden field to store the job id and deal with it, and it is readonly to avoid
changing it.

printer/views.py

@@ -59,8 +59,6 @@ def new_job(request):
                 form_kwargs={'user': request.user},
             )
 
-
-
             if job_formset.is_valid():
                 data = []
                 i=0
@@ -86,7 +84,9 @@ def new_job(request):
                     i+=1
                 job_formset_filled_in = formset_factory(PrintForm, extra=0)(
                     initial=data,
-                    form_kwargs={'user': request.user},
+                    # jids=jids,
+                    form_kwargs={'user': request.user,
+                    },
                 )
 
                 if job_formset.total_error_count() == 0:
@@ -150,6 +150,7 @@ def new_job(request):
 
     ### GET request
     else:
+        # raise Exception("Coucou2")
         job_formset = formset_factory(JobWithOptionsForm)(
             form_kwargs={'user': request.user}
         )